indexOf Examples

The general syntax for this method is:

stringName.indexOf(substr);

Given a candidate substring, this method returns the integer index of the first occurrence of the substring in the string. If the substring does not occur in the string, -1 is returned.

Example
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console.log("LaunchCode".indexOf("C"));

console.log("LaunchCode".indexOf("A"));

console.log("dogs and dogs and dogs!".indexOf("dog"));

Console Output

6
-1
0
Example

An email address must contain an @ symbol. Checking for the presence of this symbol is a part of email address verification in most programs.

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let input = "[email protected]";
let atIndex = input.indexOf("@");

if (atIndex > -1) {
   console.log("Email contains @");
} else {
   console.log("Invalid email");
}

Console Output

Email contains @