Javascript Uncaught TypeError：引用document.createElement时非法调用

Question

If I can write

var x = window.alert;
x("Hello"); //This works as expected.

Why am I not being able to write the same for document.createElement .

var h = document.createElement;
h("div"); //This line throws error 

Uncaught TypeError: Illegal invocation

Answer 1

When you call h , its context this refers to the wrong entry. You can fix this by binding it to document .

var h = document.createElement.bind(document)

alert can be called as-is, so the scope doesn't change when you alias it.