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    总结分享20个提升效率的JavaScript简写技巧

    长期闲置长期闲置2022-01-13 18:11:20转载91
    本篇文章给大家整理分享了20个提升效率的JavaScript简写技巧,希望对大家有帮助。

    简写技巧

    当同时声明多个变量时,可简写成一行

    //Longhand
    let x;
    let y = 20;
     
    //Shorthand
    let x, y = 20;

    利用解构,可为多个变量同时赋值

    //Longhand
    let a, b, c;
    a = 5;
    b = 8;
    c = 12;
    //Shorthand
    let [a, b, c] = [5, 8, 12];

    巧用三元运算符简化if else

    //Longhand 
    let marks = 26; 
    let result; 
    if (marks >= 30) {
       result = 'Pass'; 
    } else { 
       result = 'Fail'; 
    } 
    //Shorthand 
    let result = marks >= 30 ? 'Pass' : 'Fail';

    使用||运算符给变量指定默认值

    本质是利用了||运算符的特点,当前面的表达式的结果转成布尔值为false时,则值为后面表达式的结果

    //Longhand
    let imagePath;
    let path = getImagePath();
    if (path !== null && path !== undefined && path !== '') {
        imagePath = path;
    } else {
        imagePath = 'default.jpg';
    }
    //Shorthand
    let imagePath = getImagePath() || 'default.jpg';

    使用&&运算符简化if语句

    例如某个函数在某个条件为真时才调用,可简写

    //Longhand
    if (isLoggedin) {
        goToHomepage();
     }
    //Shorthand
    isLoggedin && goToHomepage();

    使用解构交换两个变量的值

    let x = 'Hello', y = 55;
    //Longhand
    const temp = x;
    x = y;
    y = temp;
    //Shorthand
    [x, y] = [y, x];

    适用箭头函数简化函数

    //Longhand
    function add(num1, num2) {
      return num1 + num2;
    }
    //Shorthand
    const add = (num1, num2) => num1 + num2;

    需要注意箭头函数和普通函数的区别

    使用字符串模板简化代码

    使用模板字符串代替原始的字符串拼接

    //Longhand
    console.log('You got a missed call from ' + number + ' at ' + time);
    //Shorthand
    console.log(`You got a missed call from ${number} at ${time}`);

    多行字符串也可使用字符串模板简化

    //Longhand
    console.log('JavaScript, often abbreviated as JS, is a\n' + 
                'programming language that conforms to the \n' + 
                'ECMAScript specification. JavaScript is high-level,\n' + 
                'often just-in-time compiled, and multi-paradigm.'
                );
    //Shorthand
    console.log(`JavaScript, often abbreviated as JS, is a
                programming language that conforms to the
                ECMAScript specification. JavaScript is high-level,
                often just-in-time compiled, and multi-paradigm.`
                );

    对于多值匹配,可将所有值放在数组中,通过数组方法来简写

    //Longhand
    if (value === 1 || value === 'one' || value === 2 || value === 'two') {
      // Execute some code
    }
    // Shorthand 1
    if ([1, 'one', 2, 'two'].indexOf(value) >= 0) {
       // Execute some code
    }
    // Shorthand 2
    if ([1, 'one', 2, 'two'].includes(value)) { 
        // Execute some code 
    }

    巧用ES6对象的简洁语法

    例如,当属性名和变量名相同时,可直接缩写为一个

    let firstname = 'Amitav';
    let lastname = 'Mishra';
    //Longhand
    let obj = {firstname: firstname, lastname: lastname};
    //Shorthand
    let obj = {firstname, lastname};

    使用一元运算符简化字符串转数字

    //Longhand
    let total = parseInt('453');
    let average = parseFloat('42.6');
    //Shorthand
    let total = +'453';
    let average = +'42.6';

    使用repeat()方法简化重复一个字符串

    //Longhand
    let str = '';
    for(let i = 0; i < 5; i ++) {
      str += 'Hello ';
    }
    console.log(str); // Hello Hello Hello Hello Hello
    // Shorthand
    'Hello '.repeat(5);
    // 想跟你说100声抱歉!
    'sorry\n'.repeat(100);

    使用双星号代替Math.pow()

    //Longhand
    const power = Math.pow(4, 3); // 64
    // Shorthand
    const power = 4**3; // 64

    使用双波浪线运算符(~~)代替Math.floor()

    //Longhand
    const floor = Math.floor(6.8); // 6
    // Shorthand
    const floor = ~~6.8; // 6

    需要注意,~~仅适用于小于2147483647的数字

    巧用扩展操作符(...)简化代码

    简化数组合并

    let arr1 = [20, 30];
    //Longhand
    let arr2 = arr1.concat([60, 80]); // [20, 30, 60, 80]
    //Shorthand
    let arr2 = [...arr1, 60, 80]; // [20, 30, 60, 80]

    单层对象的拷贝

    let obj = {x: 20, y: {z: 30}};
    //Longhand
    const makeDeepClone = (obj) => {
      let newObject = {};
      Object.keys(obj).map(key => {
          if(typeof obj[key] === 'object'){
              newObject[key] = makeDeepClone(obj[key]);
          } else {
              newObject[key] = obj[key];
          }
    });
    return newObject;
    }
    const cloneObj = makeDeepClone(obj);
    //Shorthand
    const cloneObj = JSON.parse(JSON.stringify(obj));
    //Shorthand for single level object
    let obj = {x: 20, y: 'hello'};
    const cloneObj = {...obj};

    寻找数组中的最大和最小值

    // Shorthand
    const arr = [2, 8, 15, 4];
    Math.max(...arr); // 15
    Math.min(...arr); // 2

    使用for in和for of来简化普通for循环

    let arr = [10, 20, 30, 40];
    //Longhand
    for (let i = 0; i < arr.length; i++) {
      console.log(arr[i]);
    }
    //Shorthand
    //for of loop
    for (const val of arr) {
      console.log(val);
    }
    //for in loop
    for (const index in arr) {
      console.log(arr[index]);
    }

    简化获取字符串中的某个字符

    let str = 'jscurious.com';
    //Longhand
    str.charAt(2); // c
    //Shorthand
    str[2]; // c

    移除对象属性

    let obj = {x: 45, y: 72, z: 68, p: 98};
    // Longhand
    delete obj.x;
    delete obj.p;
    console.log(obj); // {y: 72, z: 68}
    // Shorthand
    let {x, p, ...newObj} = obj;
    console.log(newObj); // {y: 72, z: 68}

    使用arr.filter(Boolean)过滤掉数组成员的值falsey

    let arr = [12, null, 0, 'xyz', null, -25, NaN, '', undefined, 0.5, false];
    //Longhand
    let filterArray = arr.filter(function(value) {
        if(value) return value;
    });
    // filterArray = [12, "xyz", -25, 0.5]
    // Shorthand
    let filterArray = arr.filter(Boolean);
    // filterArray = [12, "xyz", -25, 0.5]

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