Detailed analysis of map() and get() in jQuery

There is a concept called "array-like" under jQuery, such as $( " li " ). When a collection is obtained, there will be some attributes of the array, but instancseof Array is still false. But var a=$( "li" )##.get()Process it like this, and theninstancseof Array returns true.

Please note that adding a serial number to var a=$( "li" ).get(1) can get a single element. The nature of these elements is not jQuery objects, but It is a Js object, so jQuery methods cannot be used directly.

The function of map() mainly has two steps. The first step is to traverse, and the second step is to replace.

  $( " li " ).map( function(  ){
    return  $(this).text(  );  // 注意return关键字不可少
} )

The map is traversed first, each item returns a text() value, and then map will These values ​​automatically replace each item value in the $("li") collection, so at this time it is still an array-like (because it is still the shell of $("li")), not a real array. So adding a get() operation later will turn it into a real array, so you can use join(), a method specific to arrays.

Such as:

    $( " li " ).map( function(  ){
        return  $(this).text(  );   
    } ).get(  ).join("%")            // 拼接成字符串，中间用“%”隔开

map() and get() can also directly manipulate the array code as follows:

var arrayObj=["www","xxx","ddd"];
var ww=$.map(arrayObj,function(i){
                      return i;
              }).join(",");
console.log(ww);
var tt=$(":checkbox").map(function(){
                     return this.value;
          }).get().join(",");
console.log(tt);

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