In this tutorial, you learn how to use Javascript indexOf function with examples.
Must know about IndexOf() method
1. Using this you can find substring position inside a string or inside an array
2. This function returns -1 if the substring position not found inside string
3. Returns the index position if the substring is found at first occurence.
4. It's a case sensitive function. It means small and capital letters are treated differently.
<!DOCTYPE html>
<html>
<head>
<title>
JavaScript indexOf Method
</title>
</head>
<body>
<script>
let str ="I am a blogger"
let subString="a"
let index=str.indexOf(subString)
console.log(index);
</script>
</body>
</html>The above script returns 2 as the index position.
It's a case-sensitive function, which means uppercase letters and lowercase letters are treated differently.
Let's see another example
<!DOCTYPE html>
<html>
<head>
<title>
JavaScript indexOf Method
</title>
</head>
<body>
<script>
let str ="JavaScript a cool language"
let subString="java"
let index=str.indexOf(subString)
console.log(index);
</script>
</body>
</html>The console log will output -1 since, it can not find the sub-string "java" in it. The main string has "Java" not "java", which proves it a case-sensitive function.
Let's see another example. In this example we use an array of objects.
<!DOCTYPE html>
<html>
<head>
<title>
JavaScript indexOf Method
</title>
</head>
<body>
<script>
let fruits = ["Banana", "Orange", "Apple", "Mango"];
let index = fruits.indexOf("Apple");
console.log(index);
</script>
</body>
</html>The above JavaScript code would print 2 on the console.
So indexOf returns an index position from a string or an array objects. If it can not find it returns -1.
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