How to check if a string contains substring in Java Script?

To check this you can use String.indexOf(subString), which returns position of the first occurrence of subString or -1, if it wasn't found.

var str= 'test Text';
var subStr = 'test';
if( str.indexOf( subStr ) !== -1 ) alert( 'substring found' );

indexOf is case sensitive, to check for subString regardless of its case sensitivity you can use the following code:

var str= 'test Text';
var subStr = 'TEXT';
if( str.toLowerCase().indexOf( subStr.toLowerCase() ) !== -1 ) alert( 'substring found' );

Continue reading here: Forms in HTML5

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