is常用判断函数集合

一、javascript：typeof 返回的是字符串，有六种可能， "number"、"string"、"boolean"、"object"、"function"、"undefined"

• 是否为字符串："", "false", "0", "Hello World"

var isString = function(obj){
	return typeof obj === 'string';
}
var isString = function(obj){
    return Object.prototype.toString.call(obj) === '[object String]';
};

• 是否为布尔值：false, true

var isBoolean = function(obj){
	return typeof obj === 'boolean';
}
var isBoolean = function(obj){
    return Object.prototype.toString.call(obj) === '[object Boolean]';
};

• 是否为数值：0, 3.14, -1, NaN

var isNumber = function(obj){
	return typeof obj === 'number';
}
var isNumber = function(obj){
    return Object.prototype.toString.call(obj) === '[object Number]';
};

• 是否为undefined值

var isUndefined = function(obj){
    return typeof obj === 'undefined';
}
var isUndefined = function(obj){
    return Object.prototype.toString.call(obj) === '[object Undefined]';
};

• 是否为null值：( typeof null === 'object' )

var isNull = function(obj){
    return Object.prototype.toString.call(obj) === '[object Null]';
};

• 是否为数组：( typeof [] === 'object' )

var isArray = function(obj){
    if(Array.isArray){
        return Array.isArray(obj);
    }
    return Object.prototype.toString.call(obj) === '[object Array]';
}

• 是否为方法/函数

var isFunction = function(obj){
    return typeof obj === 'function';
}
var isFunction = function(obj){
    return Object.prototype.toString.call(obj) === '[object Function]';
}