Check if a variable is a string using JavaScript

Checking the type of a variable can be done by using typeof operator. It directly applies either to a variable name or to a variable.

Syntax:

typeof varName;

• varName: It is the name of variable.

Example 1:This Example checks if the variable boolValue and numValue is string. 

html

<h1 style="color:green;">
    GeeksForGeeks
</h1>
<p>
    var boolValue = true;
    <br>
    var numValue = 17;
</p>
<button onclick="Geeks()">
    Click to check
</button>
<p id="GFG_P" style="color:green; font-size: 20px;">
</p>
<script>
    function Geeks() {

        <!-- "boolean" value. -->
        var boolValue = true;

        <!-- "integer " value. -->
        var numValue = 17;
        var el = document.getElementById("GFG_P");
        var bool, num;

        if (typeof boolValue == "string") {
            bool = "is a string";
        } else {
            bool = "is not a string";
        }
        if (typeof numValue == "string") {
            num = "is a string";
        } else {
            num = "is not a string";
        }
        el.innerHTML = "boolValue " + bool
        + "<br>numValue " + num;

    }
</script>

Output:

Example 2:This Example checks if the variable strValue and objGFG is a string. 

html

<h1 style="color:green;">
    GeeksForGeeks
</h1>
<p>
    <!-- "String" value. -->
    var strValue =
    "This is GeeksForGeeks";
    <br>
    <!-- "Object" value. -->
    var objGFG = new String(
    "This is GeeksForGeeks" );
</p>
<button onclick="Geeks()">
    Click to check
</button>
<p id="GFG_P" style="color:green; font-size: 20px;">
</p>
<script>
    function Geeks() {
        var strValue = "This is GeeksForGeeks";
        var objGFG = new String("This is GeeksForGeeks");
        var el = document.getElementById("GFG_P");
        var str, obj;
        if (typeof strValue == 'string') {
            str = "is a string";
        } else {
            str = "is not a string";
        }
        if (typeof objGFG == "string") {
            obj = "is a string";
        } else {
            obj = "is not a string";
        }
        el.innerHTML = "strValue " + str + "<br>objGFG " + obj;

    }
</script>

Output:

Explanation: String formed using new keyword will be of object type hence objGFG doesn’t return true when compared to String.