1. The default value of a variable defined in javascript but not assigned an initial value is undefined. eg.
var testundefined;
if(undefined==testundefined){
alert("undefined==testundefined");//output undefined==testundefined
}
2.javascript null and undefined are equal.
var testNull=null;
var testundefined;
if(testNull==testundefined){
alert("undefined==testundefined");
}
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