Null and undefined analysis in JavaScript_javascript skills

1. The default value of a variable defined in javascript but not assigned an initial value is undefined.
eg.

Copy code The code is as follows:

var testundefined;
if(undefined==testundefined){
alert("undefined==testundefined");//output undefined==testundefined
}

2.javascript null and undefined are equal.

Copy code The code is as follows:

var testNull=null;
var testundefined;
if(testNull==testundefined){
alert("undefined==testundefined");
}