javaScript常用方法 - Golover's Blog

使用给定的参数对句子执行一次查找和替换，然后返回新句子#

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function myReplace(str, before, after) {
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    if (before.charAt(0) >= 'A' && before.charAt(0) <= 'Z') {
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        //将after的首字母变为大写
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        after = after.replace(after.charAt(0), after.charAt(0).toUpperCase());
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        str = str.replace(before, after);
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    } else {
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//将after的首字母变为小写
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        after = after.replace(after.charAt(0), after.charAt(0).toLowerCase());
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        str = str.replace(before, after);
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    }
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    return str;
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}
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console.log(myReplace("Let us get back to more Coding", "Coding", "algorithms"))

重复输出字符串#

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function repeat(str, num) {
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    if (num > 0) {
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        var newstr = []
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        for (let i = 0; i < num; i++) {
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            newstr[i] = str
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        }
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        console.log(newstr.join(""));
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    } else {
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        console.log(" ");
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    }
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}
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repeat("i love you ", 3);

字符串超出隐藏#

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function truncate(str, num) {
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    let newstr = str.split("");
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    if (newstr.length > num && num > 3) {
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        console.log(newstr.slice(0, num - 3).join("") + '...');
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    } else if (num <= 3) {
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        console.log(newstr.slice(0, num).join("") + '...');
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    } else if (newstr.length === num) {
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        console.log(newstr.join(""));
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    }
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    // console.log(newstr.slice(0, num).join("") + '...')
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    // return newstr1;
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}
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truncate("Walking on water and developing software from a specification", 36)

把一个数组分成子数组为n的一个2维数组#

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function chunk(arr, size) {
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    var len = arr.length;
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    var n = len / size;
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    var arry = [];
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    for (var i = 0; i < n; i++) {
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        arry[i] = arr.slice(size * i, size * (i + 1))
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    }
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    // console.log(arr.slice(2, 4))
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    console.log(arry)
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}
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chunk([0, 1, 2, 3, 4, 5], 3);

如果数组第一个字符串元素包含了第二个字符串元素的所有字符，函数返回true。#

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function mutation(arr) {
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    let arry = [];
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    let arr1 = arr[1].toLowerCase().split("")
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    let arr0 = arr[0].toLowerCase()
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    arr1.forEach((e, i) => {
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        if (arr0.indexOf(e) >= 0) {
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            arry[i] = true;
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            console.log(e, true)
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        } else {
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            console.log(e, false)
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            arry[i] = false;
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        }
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    });
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    // return arr[0].toLowerCase()
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    if (JSON.stringify(arry).indexOf('false') >= 0) {
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        return false;
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    } else {
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        return true;
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    }
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    // return arr[1].toLowerCase().split("")
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}
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yy = mutation(["floor", "for"]);

实现一个摧毁(destroyer)函数，第一个参数是待摧毁的数组，其余的参数是待摧毁的值#

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function destroyer() {
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  var argu = arguments
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  var arr1 = argu[0];
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  var arr2 = arr1.filter(function (val) {
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    var a = true;
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    for (var i = 1; i < argu.length; i++) {
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      if (val === argu[i]) {
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        a = false;
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      }
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    }
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    return a;
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  })
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  return arr2
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}
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console.log(destroyer([1, 2, 3, 1, 2, 3], 2, 3));

先给数组排序，然后找到指定的值在数组的位置，最后返回位置对应的索引。#

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function where(arr, num) {
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    function compare(a, b) {
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        return a - b;
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    }
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    arr.push(num);
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    arr.sort(compare);
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    return arr.indexOf(num);
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}
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console.log(where([2, 10, 20, 3], 5))

下面我们来介绍风靡全球的凯撒密码Caesar cipher，又叫移位密码。移位密码也就是密码中的字母会按照指定的数量来做移位。#

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// 普通方法
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function rot13(str) { // LBH QVQ VG!
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    var yy = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'];
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    var ystr = yy.join("").replace(",", "");
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    let n = [];
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    str.toUpperCase().split("").forEach(e => {
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        if (e === "!" || e === '?' || e === " " || e === ".") n.push(e)
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        n.push(ystr.indexOf(e))
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    })
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    let newstr = [];
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    n.forEach((e, i) => {
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        if (e === "!" || e === '?' || e === " " || e === ".") {
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            newstr[i] = e;
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        } else if (e >= 0) {
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            newstr[i] = yy[e + 13];
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            if (e + 13 > 25) {
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                newstr[i] = yy[13 - (26 - e)]
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            }
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        }
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    })
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    return newstr.join("");
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}
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// charCodeAt() 方法可返回指定位置的字符的 Unicode 编码。这个返回值是 0 - 65535 之间的整数。
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// (字符串中第一个字符的下标是 0。如果 index 是负数，或大于等于字符串的长度，则 charCodeAt() 返回 NaN。)
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// fromCharCode() 可接受一个指定的Unicode 值，然后返回一个字符串。
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// (该方法是 String 的静态方法，字符串中的每个字符都由单独的数字 Unicode 编码指定。
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// 它不能作为您已创建的 String 对象的方法来使用。因此它的语法应该是
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// String.fromCharCode()，而不是 myStringObject.fromCharCode()。)
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function rot13(str) { // LBH QVQ VG!
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    var str1 = [];
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    for (var i = 0; i < str.length; i++) {
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        var num = str[i].charCodeAt();
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        if (num >= 65 && num <= 77) {
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            num += 13;
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        } else if (num > 77 && num < 91) {
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            num -= 13;
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        }
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        str1.push(String.fromCharCode(num));
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    }
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    return str1.join("");
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}
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console.log(rot13("GUR DHVPX OEBJA QBT WHZCRQ BIRE GUR YNML SBK."))

求任意两数之间所有数之和#

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function sumAll(arr) {
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    var i = 0;
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    let a = Math.max(...arr);
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    let b = Math.min(...arr);
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    for (; b < a + 1; b++) {
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        i = i + b
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    }
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    console.log(i)
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}
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sumAll([56, 10]);

数组去重#

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function diff(arr1, arr2) {
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  var newArr = [];
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  newArr = Array.from(new Set([...arr1, ...arr2]));
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  console.log(newArr);
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}
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diff(["diorite", "andesite", "grass", "dirt", "pink wool", "dead shrub"], ["diorite", "andesite", "grass", "dirt", "dead shrub"]);

对象数组去重#

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const lists = [{ id: 1, a: 1 }, { id: 2, a: 2 }, { id: 3, a: 3 }, { id: 4, a: 4 }, { id: 1, a: 1 }, { id: 2, a: 2 }, { id: 1, a: 1 }, { id: 2, a: 2 }, { id: 3, a: 3 }, { id: 4, a: 4 }, { id: 1, a: 1 }, { id: 2, a: 2 }];
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const lists2 = [{ id: 1, a: 1 }, { id: 2, a: 2 }, { id: 3, a: 3 }, { id: 4, a: 4 }, { id: 1, a: 1 }, { id: 2, a: 2 }];
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const result = lists.reduce((prev, cur) => {
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  const ids = prev.map(item => item.id)
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  return ids.includes(cur.id) ? prev : [...prev, cur]
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}, []);
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console.log(result)

比较两个数组，然后返回一个新数组，该数组的元素为两个给定数组中所有独有的数组元素。换言之，返回两个数组的差异。#

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function diff(arr1, arr2) {
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  var newArr = [];
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  var arr3 = [...arr1, ...arr2]
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  // var arr3 = arr1.concat(arr2); //将arr1和arr2合并为arr3
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  function isContain(a) {
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    //找出arr3中不存在于arr1和arr2中的元素
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    return arr1.indexOf(a) == -1 || arr2.indexOf(a) == -1;
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  }
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  newArr = arr3.filter(isContain);
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  console.log(newArr);
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}
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diff(["andesite", "grass", "dirt", "pink wool", "dead shrub"], ["diorite", "andesite", "grass", "dirt", "dead shrub"])

将给定的数字转换成罗马数字。#

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function convert(num) {
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  var num0 = ["1", "4", "5", "9", "10", "40", "50", "90", "100", "400", "500", "900", "1000"];
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  var num0R = num0.reverse();
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  var num1 = ["I", "IV", "V", "IX", "X", "XL", "L", "XC", "C", "CD", "D", "CM", "M"];
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  var num1R = num1.reverse();
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  var numCon = [];
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  num0R.forEach(function (value, index, arr) {
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    while (num >= value) { //条件循环
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      numCon.push(num1R[index]);
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      num -= value;
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    }
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  });
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  return numCon.join("");
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}
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console.log(convert(222));

将给的的数字转换成中文#

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function convert(num) {
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  let changeNum = [ '零', '一','二','三','四','五','六', '七','八', '九' ];
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  let unit = ['', '十', '百', '千', '万'];
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  num = parseInt(num)
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  let getWan = temp => {
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    let strArr = temp
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      .toString()
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      .split('')
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      .reverse()
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    let newNum = ''
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    for (var i = 0; i < strArr.length; i++) {
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      newNum =
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        (i == 0 && strArr[i] == 0
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          ? ''
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          : i > 0 && strArr[i] == 0 && strArr[i - 1] == 0
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            ? ''
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            : changeNum[strArr[i]] + (strArr[i] == 0 ? unit[0] : unit[i])) +
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        newNum
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    }
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    return newNum
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  }
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  let overWan = Math.floor(num / 10000)
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  let noWan = num % 10000
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  if (noWan.toString().length < 4) {
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    noWan = '0' + noWan
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  }
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  return overWan ? getWan(overWan) + '万' + getWan(noWan) : getWan(num)
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}

遍历一个对象数组（第一个参数）并返回一个包含相匹配的属性#

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function where(collection, source) {
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  var arr = [];
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  // What's in a name?
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  var sourceArr = Object.keys(source);
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  arr = collection.filter(function (obj) {
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    for (var i = 0; i < sourceArr.length; i++) {
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      if (obj[sourceArr[i]] !== source[sourceArr[i]]) {
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        return false;
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      }
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    }
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    return true;
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  });
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  console.log(arr);
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}
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where([{
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  first: "Romeo",
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  last: "Montague"
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}, {
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  first: "Mercutio",
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  last: null
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}, {
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  first: "Tybalt",
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  last: "Capulet"
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}], {
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  last: "Capulet"
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});

给定一个字符串返回对象数组中包含该字符串的对象#

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let str = 'MOTI';
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let data = [
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    { technology: 'CHARACTER', score: -1, text: 'sfoefjlasdoejfoausfe' },
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    { technology: 'PRESSURE_RELIEF', score: 2, text: '123qw' },
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    { technology: 'SUPPORT', score: 3, text: '123qw' },
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    { technology: 'MOTION_ISOLATION', score: 2, text: '123qw' },
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    { technology: 'TEMPERATURE_MANAGEMENT', score: -1, text: '123qw' },
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    { technology: 'COMFORT', score: 2, text: 'szyy' }
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];
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let result = data.filter(function (el) {
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    return el.technology.indexOf(str) > -1 || el.text.indexOf(str) > -1;
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});
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console.log(result);
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Javascript
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function confirmEnding(str, target) {
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    var n = target.split("").length;
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    var newstr = str.split(" ").join("");
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    if (newstr.substr(-n) === target) {
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        console.log(newstr.substr(-n));
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        // return true;
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    } else {
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        //return false;
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        console.log(newstr.substr(-n));
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    }
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}
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confirmEnding("Walking on water and developing software from a specification are easy if both are frozen", "specification");