'hello world hello'.indexOf('o', -5) returns 4 - because it causes the method to behave as if the second argument were 0, and the first occurrence of o at a position greater or equal to 0 is at position 4.

If position is less than zero, the method behaves as it would if position were 0. If position is greater than the length of the calling string, the method doesn't search the calling string at all. The method returns the index of the first occurrence of the specified substring at a position greater than or equal to position, which defaults to 0. All values are coerced to strings, so omitting it or passing undefined causes indexOf() to search for the string 'undefined', which is rarely what you want. Object.prototype._lookupSetter_() Deprecated.Object.prototype._lookupGetter_() Deprecated.Object.prototype._defineSetter_() Deprecated.Object.prototype._defineGetter_() Deprecated.‘amtrack’.indexOf(‘a’) // 0 – Javascript string contains character check Read: How to remove a property from a Javascript Object

You can also pass an optional second parameter to indicate where to start searching. This method returns an integer with the position of the substring, and if it does not find the substring, it returns -1. ‘AMTRACK’.includes(‘M’, 1) // true Using the indexOf () methodīefore the release of the official method includes(), another way to check if a string contains a substring was to use the method indexOf(). You can optionally pass a second parameter to indicate where to start looking for the substring: Read: How to delete values from an array in Javascript ‘HI WORLD’.toLowerCase().includes(‘world’) // true – javascript string lowercase Note that the method includes()is case sensitive, so if you want to search for an independent string if it is uppercase or lowercase, you can do the following: ‘Hi world’.includes(‘world’) // true – javascript includes string method The method includes()is the official way to check if a string is contained within another string. In JavaScript there are several ways to check whether a string contains a word or a substring. Checking if a string contains a word is a common task in any programming language.

Javascript if string contains