for循環(huán)

var x = 0;
var i;
for (i=1; i<=10000; i++) {
    x = x + i;
}
x; // 50005000

遍歷數(shù)組

var arr = ['Apple', 'Google', 'Microsoft'];
var i, x;
for (i=0; i<arr.length; i++) {
    x = arr[i];
    alert(x);
}

退出循環(huán) break

for ... in

把一個對象的所有屬性依次循環(huán)出來

var o = {
    name: 'Jack',
    age: 20,
    city: 'Beijing'
};
for (var key in o) {
    alert(key); // 'name', 'age', 'city'
}

var o = {
    name: 'Jack',
    age: 20,
    city: 'Beijing'
};
for (var key in o) {
    if (o.hasOwnProperty(key)) {
        alert(key); // 'name', 'age', 'city'
    }
}

for ... in對Array的循環(huán)得到的是String而不是Number

var a = ['A', 'B', 'C'];
for (var i in a) {
    alert(i); // '0', '1', '2'
    alert(a[i]); // 'A', 'B', 'C'
}

練習(xí)

'use strict';
var arr = ['Bart', 'Lisa', 'Adam'];
for(var i in arr)
{
  alert('Hello,'+arr[i]+"!");
}