'12'

12

'12px'

12

'0x12'

0

function parse2Int(num) {
    var type = typeof num;
    if (type === "number") {
        if (num % 1 === 0) {
            return num;
        } else {
            return num-num%1;
        }
    } else if (type === "string") {
        var s = "", n0 = "0".charCodeAt(0), n9 = "9".charCodeAt(0);
        for (var i = 0; i < num.length; i++) {
            var c = num.charCodeAt(i);
            if (n0 <= c && c <= n9) {
                s += num.charAt(i);
            } else {
                break;
            }
        }
        function s2i(s) {
            var n = 0, n0 = "0".charCodeAt(0);
            for (var i = 0; i < s.length; i++) {
                n = 10*n + (s.charCodeAt(i)-n0);
            }
            return n;
        }
        return s2i(s);
    }
    return NaN;
}

* 流程控制

实现 fizzBuzz 函数，参数 num 与返回值的关系如下：
1、如果 num 能同时被 3 和 5 整除，返回字符串 fizzbuzz
2、如果 num 能被 3 整除，返回字符串 fizz
3、如果 num 能被 5 整除，返回字符串 buzz
4、如果参数为空或者不是 Number 类型，返回 false
5、其余情况，返回参数 num

Input:15 Output: fizzbuzz

function fizzBuzz(num) {
    if (!num) {return !1;}
    if (typeof num === "number") {
        var a = num%3===0, b = num%5==0;
        return a&&b ? "fizzbuzz" : a ? "fizz" : b ? "buzz" : num;
    }
    return !1;
}

* 求 a 和 b 相乘的值，a 和 b 可能是小数，需要注意结果的精度问题

input: 3, 0.0001

output: 0.0003

function multiply(a, b) {
    var d1 = d2 = 0;
    while (a%1 !== 0) {
        a *= 10;
        d1++;
    }
    while (b%1 !== 0) {
        b *= 10;
        d2++;
    }
    var d = d1+d2;
    return parseFloat(a * b * Math.pow(0.1, d)).toFixed(d);
}

javascript对象克隆:

Object.prototype.clone = function() {
    // Handle null or undefined or function
    if (null == this || "object" != typeof this)
        return this;
    // Handle the 3 simple types, Number and String and Boolean
    if(this instanceof Number || this instanceof String || this instanceof Boolean)
        return this.valueOf();
    // Handle Date
    if (this instanceof Date) {
        var copy = new Date();
        copy.setTime(this.getTime());
        return copy;
    }
    // Handle Array or Object
    if (this instanceof Object || this instanceof Array) {
        var copy = (this instanceof Array)?[]:{};
        for (var attr in this) {
            if (this.hasOwnProperty(attr))
                copy[attr] = this[attr]?this[attr].clone():this[attr];
        }
        return copy;
    }
    throw new Error("Unable to clone obj! Its type isn't supported.");
}

但是这样写会与jQuery冲突

为了不污染原型链

function clone(o) {
    // Handle null or undefined or function
    if (null == o || "object" != typeof o)
        return o;
    // Handle the 3 simple types, Number and String and Boolean
    if(o instanceof Number || o instanceof String || o instanceof Boolean)
        return o.valueOf();
    // Handle Date
    if (o instanceof Date) {
        var copy = new Date();
        copy.setTime(o.getTime());
        return copy;
    }
    // Handle Array or Object
    if (o instanceof Object || o instanceof Array) {
        var copy = (o instanceof Array)?[]:{};
        for (var attr in o) {
            if (o.hasOwnProperty(attr))
                copy[attr] = o[attr]? clone(o[attr]):o[attr];
        }
        return copy;
    }
    throw new Error("Unable to clone obj! Its type isn't supported.");
}