If substring in string, remove it through the end from string

Question

I'm trying to figure out how to do the following with javascript:
If a substring is in the string, remove from the beginning of the substring till the end of the string from the string.

For example (pseudocode):

var mySub = 'Foo'
var myString = 'testingFooMiscText'
var myString2 = 'testingMisctext'

var myStringEdit = //myString - (Foo till end myString)
var myString2Edit = myString2 //(cause no Foo in it)

Answer 1

var index = str.indexOf(str1);
if(index != -1)
    str = str.substr(index) 

Answer 2

If I understand what you're asking, you'll want to do this:

function replaceIfSubstring(original, substr) {
    var idx = original.indexOf(substr);
    if (idx != -1) {
        return original.substr(idx);
    } else {
        return original;
    }
}