JS中位运算符的一些妙用

	1 << 2  // 4, 即 2的2次方
	1 << 10 // 1024, 即 2的10次方
	
	// 但是要注意使用场景
	a = 2e9;   // 2000000000
	a << 1;    // -294967296

	// --- before ---
    // if 判断
    if (toggle) {
        toggle = 0;
    } else {
        toggle = 1;
    }
    // 三目运算符
    togle = toggle ? 0 : 1;
    
    // --- after ---
    toggle ^= 1;

	console.log(7 & 1);    // 1
    console.log(8 & 1) ;   // 0

	console.log(!!7);       // true
    console.log(!!0);       // false
    console.log(!!-1);      // true
    console.log(!!0.71);    // true

	console.log(~~11.71)     // 11
    console.log(11.71 >> 0)  // 11
    console.log(11.71 << 0)  // 11
    console.log(11.71 | 0)   // 11
    console.log(11.71 >>> 0) // 11

	// --- before ---
    let temp = a; a = b; b = temp; // 传统，但需要借助临时变量
    b = [a, a = b][0] // 借助数组
    
    // --- after --- 只能用于整数
    let a = 7
    let b = 1
    a ^= b
    b ^= a
    a ^= b
    console.log(a)   // 1
    console.log(b)   // 7
    
    [a, b] = [b, a]; // ES6，解构赋值

	(a ^ b) >= 0; //  true 相同; false 不相同

	// --- before ---
    if (a !== 1171) {...};
    
    // --- after ---
    if (a ^ 1171) {...};

	Math.random().toString(16).substring(2, 15);

	// --- before ---
    "alpha,bravo,charlie".split(",");
    
    // --- after ---
    "alpha0bravo0charlie".split(0);

	// --- before ---
    let b = `<a herf="www.google.com">google</a>`;
    
    // --- after ---
    let b =  google .link( www.google.com );

    // --- before ---
    for (let a = "", i = 7; i--;) a+= 0;
    
    // --- after ---
    let b = Array(7).join(0); // "0000000"let c = Array(7).join( La ) // "LaLaLaLaLaLa"
    
    // ES6
    let d = "0".repeat(7); // "0000000"

    // --- before ---
    let b = 0 | Math.random() * 100
    
    // --- after ---
    let a;
    a = new Date % 100; // 两位随机数
    a = new Date % 1000; // 三位随机数
    a = new Date % 10000; // 四位随机数...依次类推
    // 不要在快速循环中使用，因为毫秒可能没有变化；

    // --- before ---
    for(let i = 0; i < arr.length; i++) {...}
    
    // --- after ---
    for(let i = arr.length; i--;) {...} // 注意 i-- 后面的分号别漏了