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function sum(num1,num2) {
return num1+num2;
}
function callsum(num1,num2) {
return sum.apply(this,arguments)
}
alert(callsum(1,2)); //3

callsum内部的sum.apply(this,arguments)中this指代的是什么？我知道单单在全局执行sum.apply(this,arguments),this代表window,但到了函数里面this是什么呢？

8 years, 11 months ago

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倚窗听雪白 8 years, 11 months ago

Answer 1

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answered 8 years, 11 months ago

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天下真爛漫 answered 8 years, 11 months ago

Answer 2

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window.alert(callsum(1,2));

answered 8 years, 11 months ago

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黑猫D野望 answered 8 years, 11 months ago

Answer 3

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this为调用所在函数的对象，如果这个对象为null/undefined,那么指向window全局对象

answered 8 years, 11 months ago

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最爱的唯一 answered 8 years, 11 months ago

Answer 4

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大家遗漏了一点，在es5严格模式下，函数中的this 是undefined

answered 8 years, 11 months ago

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wlwllq answered 8 years, 11 months ago

Answer 5

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在这个例子里 this 依然是 window，因为调用 callsum() 的时候没有上下文（context）（更正一下：上下文是 window）。如果是：


 var a = {};
a.fun = callsum;
a.fun();

这时候 callsum 里的 this 指向 a

answered 8 years, 11 months ago

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宫本蕾貝卡 answered 8 years, 11 months ago