js学习之类型识别

用来判别类型的方法有好多，整理了一下4种方法，平时用的时候，在不同情景下，还是要结合着使用的。

方法一

typeof：可以识别标准类型，除了Null；不能识别具体的对象类型，除了Function

<script>
    var t = typeof(1);
    console.log(t); // t==="number"

    var t = typeof(new Number(1))
    console.log(t); // t==="object"

    var t = typeof("abc");
    console.log(t); // t==="string"

    var t = typeof(new String("abc"));
    console.log(t); // t==="object"

    var t = typeof(true);
    console.log(t); // t==="boolean"

    var t = typeof(undefined);
    console.log(t); // t==="undefined"

    var t = typeof(null);
    console.log(t); // t==="object"

    var t = typeof({});
    console.log(t); // t==="object"

    var t = typeof([]);
    console.log(t); // t==="object"

    var t = typeof(new Date);
    console.log(t); // t==="object"

    var t = typeof(/d/);
    console.log(t); // t==="object"

    var t = typeof(function(){});
    console.log(t); // t==="function"
</script>

方法二

instanceof：可以识别内置对象类型，不能识别原始类型，可以识别自定义对象类型

<script>
    var t = new Number(1);
    console.log(1 instanceof Number); // false
    console.log(1 instanceof Object); // false
    console.log(t instanceof Number); // true
    console.log(t instanceof Object); // true

    var t = new String("abc");
    console.log("abc" instanceof String); // false
    console.log("abc" instanceof Object); // false
    console.log(t instanceof String); // true
    console.log(t instanceof Object); // true
    
    console.log(true instanceof Boolean); // false
    console.log(true instanceof Object); // false

    console.log(undefined instanceof Object); // false
    console.log(undefined instanceof Undefined); // Uncaught ReferenceError: Undefined is not defined
    
    console.log(null instanceof Object); // false
    console.log(null instanceof Null); // Uncaught ReferenceError: Undefined is not defined

    var t = new Object({});
    console.log(t instanceof Object); // true
    console.log({} instanceof Object); // true

    var t = new Array([]);
    console.log(t instanceof Array); // true
    console.log(t instanceof Object); // true
    console.log([] instanceof Array); // true
    console.log([] instanceof Object); // true

    var t = new Date();
    console.log(t instanceof Date); // true
    console.log(t instanceof Object); // true

    console.log(/d/ instanceof Object); // true
    console.log(/d/ instanceof Regexp); // Uncaught ReferenceError: Undefined is not defined

    var t = function(){};
    console.log(t instanceof Function); // true
    console.log(t instanceof Object); // true
</script>

方法三：可以识别标准类型以及内置对象类型，不能识别自定义类型

    function type(obj){
    return Object.prototype.toString.call(obj).slice(8,-1);
    }

示例：

<script>
    var t = type(1);
    console.log(t); // t==="Number"

    var t = type(new Number(1));
    console.log(t); // t==="Number"

    var t = type("abc");
    console.log(t); // t==="String"

    var t = type(new String("abc"));
    console.log(t); // t==="String"

    var t = type(true);
    console.log(t); // t==="Boolean"

    var t = type(undefined);
    console.log(t); // t==="Undefined"

    var t = type(null);
    console.log(t); // t==="Null"

    var t = type({});
    console.log(t); // t==="Object"

    var t = type([]);
    console.log(t); // t==="Array"

    var t = type(new Date);
    console.log(t); // t==="Date"

    var t = type(/d/);
    console.log(t); // t==="Regexp"

    var t = type(function(){});
    console.log(t); // t==="Function"
    
    function add(){};
    var f = new add();
    var t = type(f);
    console.log(t); // t==="Object"
</script>

方法四：可以识别所有类型：标准类型、内置对象类型、自定义对象类型

        function getConstructorName(obj){
    return (obj===undefined||obj===null)?obj:(obj.constructor&&obj.constructor.toString().match(/functions*([^(]*)/)[1]);
    }

示例：

<script>
    var t = getConstructorName(1);
    console.log(t); // t==="Number"

    var t = getConstructorName(new Number(1));
    console.log(t); // t==="Number"

    var t = getConstructorName("abc");
    console.log(t); // t==="String"

    var t = getConstructorName(new String("abc"));
    console.log(t); // t==="String"

    var t = getConstructorName(true);
    console.log(t); // t==="Boolean"

    var t = getConstructorName(undefined);
    console.log(t); // t==="undefined"

    var t = getConstructorName(null);
    console.log(t); // t==="null"

    var t = getConstructorName({});
    console.log(t); // t==="Object"

    var t = getConstructorName([]);
    console.log(t); // t==="Array"

    var t = getConstructorName(new Date);
    console.log(t); // t==="Date"

    var t = getConstructorName(/d/);
    console.log(t); // t==="Regexp"
    
    var t = getConstructorName(function(){});
    console.log(t); // t==="Function"
    
    function add(){};
    var f = new add();
    var t = getConstructorName(f);
    console.log(t); // t==="add"
</script>

Demo:

输入任意格式的年月日，均返回 Date 格式：

/*
* 输入格式：
* '2016-11-06'
* 1478401733333
* {y:2016,m:11,d:6}
* [2016,11,6]
* 返回格式：Date
*/
function toDate(param){
  if (typeof(param) == 'string' || 
      typeof(param) == 'number' ){
    return new Date(param);
  } 
  if (param instanceof Array){
    var date = new Date(0);
    date.setYear(param[0]);
    date.setMonth(param[1]-1);
    date.setDate(param[2]);
    return date;
  }
  if (typeof(param) == 'object') {
    var date = new Date(0);
    date.setYear(param.y);
    date.setMonth(param.m-1);
    date.setDate(param.d);
    return date;
  }
  return -1;
}