JavaScript的in操作符可以用来判断一个属性是否属于一个对象,也可以用来变量一个对象的属性
1. 判断属性属于对象
var mycar = {make: "Honda", model: "Accord", year: 1998}; //注意,属性名必须是字符串形式,因为make不是一个变量 if ( "make" in mycar ){ document.write(‘true‘); } else{ document.write(‘false‘); // 显示true }
2. for in遍历对象属性
var mycar = {make: "Honda", model: "Accord", year: 1998}; for(var p in mycar){ console.log(p + ‘: ‘ + make[p]); }
3. in可以用来进行判断
if ( foo == ‘bar‘ || foo == ‘foobar‘ || foo == ‘foo‘ ) { //... } //就可以写成: if ( foo in { ‘bar‘:‘‘, ‘foobar‘:‘‘, ‘foo‘:‘‘ } ) { //... }
4. delete操作符可以删除属性,配合in使用
var mycar = {make: "Honda", model: "Accord", year: 1998}; delete mycar.make; "make" in mycar; // returns false var trees = new Array("redwood", "bay", "cedar", "oak", "maple"); delete trees[3]; 3 in trees; // returns false
5. 尽量不要用for in遍历数组
集合遍历的效率为:hash > for(;;) > for(in)
集合相关操作首选对象,次之用for循环遍历。
参考:http://www.linuxfly.org/post/524/
原文地址:https://www.cnblogs.com/mengff/p/9603590.html
时间: 2024-10-13 23:37:36