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Summary of js loop

高洛峰
Release: 2016-10-08 16:29:25
Original
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js原生的循环有两种,一般的for循环和for...in循环。还有一种常用jQuery.each()循环。
一. js原生循环
a. for循环,代码如下:
var myArray = [1,2,3];
for (var i = 0; i < myArray.length; i++) {
    console.log(myArray[i]);
};
console:
1,2,3
b. for...in循环,代码如下:
var myArray  = [1,2,3];
for (var arr in myArray ) {
    console.log(arr);
};
console:
1,2,3
c.  for和for...in的共同点:
都可以用于数组的循环
d.  for和for...in的不同点:
for...in循环除用于数组的循环外,还可以用于对象的key循环,代码如下:
var myObject = {"id":"1","name":"john"};
for (var obj in myObject) {
    console.log(obj);
};
console:
id,name
e. 控制循环语句
break;跳出这个循环
continue;跳出本次循环
while循环:
 var cars=["BMW","Volvo","Saab","Ford"];
  var i=0;
  while (cars[i])
  {
     console.log(cars[i] + "<br>");
     i++;
  }
console:
BMW Volvo Saab Ford
do-while循环:
  var x="";
  var i= 0;
  do{
     x=x + "该数字为 " + i + "<br>";
      i++;
      console.log(x);
  }
  while (i<5) 
 
二. jQuery.each()循环
a. 遍历DOM节点   代码如下:
<ul>
  <li>a</li>
  <li>b</li>
  <li>c</li>
</ul>
 $("li").each(function(){
    alert($(this).text())
  });
b. 遍历数组
 var arr = [1,2,3];
 $.each(arr,function(i){
  console.log((arr[i]));
 });
console:
1,2,3
c. 循环对象
var myObject = {"one":1,"two":2,"three":3};
 $.each(myObject,function(i){
    console.log(myObject[i]);
 });
console:
1,2,3
 
d. 循环二维数组,代码如下: 
var myArray = [[1,2,3],[4,5,6],[7,8,9]];
 $.each(myArray,function(i,item){
    console.log(item[0]);
 });
console:
1,4,7
e. 循环控制语句:
return false;跳出这个循环
return true;继续下一个循环
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