1. Preparation, header.js a new file in the src directory shown in FIG.
2. Event bindings with on + Event name:
The first: an ordinary function bindings
The second: the arrows function
Third: function parameter passing arrow
Fourth: function does not pass parameters
Written in the constructor:
In the render function written above
Fifth: function does not pass parameters
Written render above
Sixth: pass function parameters
Seventh: transfer function parameters, and changing the content change element
Eighth:
