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曹执星-exercise4 #132

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62 changes: 62 additions & 0 deletions package-lock.json
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12 changes: 8 additions & 4 deletions test/test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,8 @@ describe('this', function () {
say: function () {
setTimeout(() => {
// this 是什么？想想为什么？
this.should.equal(null)
// this指向say,箭头函数是根据当前的词法作用域来决定this。
this.should.equal(obj)
done()
}, 0)
}
Expand All @@ -15,7 +16,8 @@ describe('this', function () {
it('global', function () {
function test() {
// this 是什么？想想为什么？
this.should.equal(null)
// this指向window，这个是使用了默认绑定，绑定到了全局对象。node环境中为global
this.should.equal(global)
}
test()
})
Expand All @@ -26,7 +28,8 @@ describe('this', function () {
say: function () {
function _say() {
// this 是什么？想想为什么？
this.should.equal(null)
// bind在绑定的对象为undefined的时候，默认是绑定全局对象
this.should.equal(global)
}
return _say.bind(obj)
}()
Expand All @@ -39,7 +42,8 @@ describe('this', function () {
obj.say = function () {
function _say() {
// this 是什么？想想为什么？
this.should.equal(null)
// bind 把this指向了obj
this.should.equal(obj)
}
return _say.bind(obj)
}()
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