JS 中在严格模式下 this 的指向问题

"use strict";
 
console.log("严格模式");
console.log("在全局作用域中的this");
console.log("this.document === document",this.document === document);
console.log("this === window",this === window);
this.a = 9804;
console.log('this.a === window.a===',window.a);

"use strict";
 
console.log("严格模式");
console.log('在全局作用域中函数中的this');
function f1(){
console.log(this);
}
 
function f2(){
function f3(){
console.log(this);
}
f3();
}
f1();
f2();

"use strict";
 
console.log("严格模式");
console.log("在对象的函数中的this");
var o = new Object();
o.a = 'o.a';
o.f5 = function(){
return this.a;
}
console.log(o.f5());

"use strict";
 
console.log("严格模式");
console.log("构造函数中的this");
function constru(){
this.a = 'constru.a';
this.f2 = function(){
console.log(this.b);
return this.a;
}
}
var o2 = new constru();
o2.b = 'o2.b';
console.log(o2.f2());

"use strict";
 
function blue_it(e){
if(this === e.target){
this.style.backgroundColor = "#00f";
}
}
var elements = document.getElementsByTagName('*');
for(var i=0 ; i<elements.length ; i++){
elements[i].onclick = blue_it;
}
 
//这段代码的作用是使被单击的元素背景色变为蓝色

<button onclick="alert((function(){'use strict'; return this})());">
内联事件处理1
</button>
<!-- 警告窗口中的字符为undefined -->
 
<button onclick="'use strict'; alert(this.tagName.toLowerCase());">
内联事件处理2
</button>
<!-- 警告窗口中的字符为button -->

 <script>
        'use strict'
      setTimeout(function(){
        console.log(this);
      },1000)
    </script>
//Window {window: Window, self: Window, document: document, name: '', location: Location, …}