要知道在javascript中this是種很神奇的東西，但是有時候也很淘氣；

如下：

<script>
    var obj = {
        name: ‘tqt‘,
        friends: [‘shangs‘, ‘lisi‘],
        sayHello: function() {
            this.friends.forEach(function(friend){
                console.log(this.name + ‘ say hello to ‘ + friend);
            });
        },
    }
    obj.sayHello();
    
 
//say hello to shangs
    //say hello to lisi
</script>

此時this已經不再指向obj了所以不會有name屬性；（this現在指向window，太淘氣了！）

對於這種情況解決辦法如下：

方法一：

<script>
    var obj = {
        name: ‘tqt‘,
        friends: [‘shangs‘, ‘lisi‘],
        sayHello: function() {
            var that = this;
            this.friends.forEach(function(friend){
                console.log(that
 
.name + ‘ say hello to ‘ + friend);
            });
        },
    }
    obj.sayHello();
    //tqt say hello to shangs
    //tqt say hello to lisi
</script>

方法二：

<script>
    var obj = {
        name: ‘tqt‘,
        friends: [‘shangs‘, ‘lisi‘],
        sayHello: function() {
            this
 
.friends.forEach(function(friend){
                console.log(this.name + ‘ say hello to ‘ + friend);
            }.bind(this));
        },
    }
    obj.sayHello();
    //tqt say hello to shangs
    //tqt say hello to lisi
</script>

方法三：

<script>
    var obj = {
        name: ‘tqt‘,
        friends: [‘shangs‘, ‘lisi‘],
        sayHello: function() {
            this.friends.forEach(function(friend){
                console.log(this.name + ‘ say hello to ‘ + friend);
            }, this);
        },
    }
    obj.sayHello();
    //tqt say hello to shangs
    //tqt say hello to lisi
</script>

方法中的函數會掩蓋this，解決辦法！