How to check if a string array contains one string in JavaScript?

There is an indexOf method that all arrays have (except in old version of Internet Explorer) that will return the index of an element in the array, or -1 if it's not in the array:

if (yourArray.indexOf("someString") > -1) {
    //In the array!
} else {
    //Not in the array
}

If you need to support old IE browsers, you can use polyfill this method using the code in the MDN article.

You can use the indexOfmethod and "extend" the Array class with the method contains like this:

Array.prototype.contains = function(element){
    return this.indexOf(element) > -1;
};

with the following results:

["A", "B", "C"].contains("A") equals true

["A", "B", "C"].contains("D") equals false

var stringArray = ["String1", "String2", "String3"];

return (stringArray.indexOf(searchStr) > -1)

Create this function prototype:
    Array.prototype.contains = function ( needle ) {
       for (i in this) {
           if (this[i] == needle) return true;
       }
       return false;
    }

and then you can use following code to search in array x

if (x.contains('searchedString')) {
    // do a
}
else
{
      // do b
}

This will do it for you:

function inArray(needle, haystack) {
    var length = haystack.length;
    for(var i = 0; i < length; i++) {
        if(haystack[i] == needle)
            return true;
    }
    return false;
}

I found it in Stack Overflow question JavaScript equivalent of PHP's in_array().