how to use the replace method in javascript?

using this example replace the __c and _ character from the string value.

here “Is_De_mo__c”, i want to remove the _ and __c, using below code we can achieve:

<script>
var tempReplace = “”;
var myOldString = “Is_De_mo__c”;
var myNewString = myOldString.replace(/__c/g, tempReplace);

var tempReplace1 =  ” “;
var myNewString1 = myNewString.replace(/_/g, tempReplace1);
document.write(“<br />New string = ” + myNewString1);
</script>