JavaScript骚操作之操作符

三目运算符 ?:

if (hasMoney) {
    console.log('周末嗨翻天');
} else {
    console.log('周末睡一天');
}

hasMoney ? console.log('周末嗨翻天') : console.log('周末睡一天');

let weekendPlan = hasMoney ? '周末嗨翻天' : '周末睡一天';

逻辑与操作符 &&

if (hasMoney) {
    console.log('周末嗨翻天');
}

hasMoney ? console.log('周末嗨翻天') : undefined;

hasMoney && console.log('周末嗨翻天');

true && console.log('It is true');                         // It is true
true && false && console.log('It is true');                // 返回 false
true && 0 && console.log('It is true');                    // 返回 0
true && undefined == null && console.log('It is true');    // It is true, 表达式undefined == null的运算结果为true
true && undefined === null && console.log('It is true');   // 返回 false, 表达式undefined === null的运算结果为false

逻辑或操作符 ||

// 当自身为undefined时，赋值为0，否则还是赋值为自身
    val = val !== undefined ? val : 0;

val = val || 0;

// ES5设置函数默认值
    function testFunc(arg1) {
        arg1 = arg1 || 1;

        // do something else
    }

    let a = 1,
        b = 2,
        c = null;

    console.log(a || b || c);         // 1
    console.log(0 || b || c);         // 2
    console.log(0 || false || c);     // null

按位取反操作符 ~

let arr = ['we', 'are', 'the', 'BlackGold', 'team'];

arr.includes('the') && console.log('in');      // in

let arr = ['we', 'are', 'the', 'BlackGold', 'team'];

arr.includes(element => element === 'the') && console.log('in');     // 返回false

let arr = ['we', 'are', 'the', 'BlackGold', 'team'];

arr.findIndex(element => element === 'the') !== -1 && console.log('in');      // in

let arr = ['we', 'are', 'the', 'BlackGold', 'team'];

~arr.findIndex(element => element === 'we') && console.log('in');      // in
~arr.findIndex(element => element === 'the') && console.log('in');      // in

console.log(~-1);       // 0 转换为Boolean值即为false
console.log(~0);        // -1 转换为Boolean值即为true
console.log(~1);        // -2 转换为Boolean值即为true