How to Determine if a Variable is a String in JavaScript?

How to Check if a Variable is a String in JavaScript

In JavaScript, variables can hold different data types, including strings. To determine whether a particular variable contains a string or any other type, you can use the following methods:

Typeof Operator

The typeof operator returns the type of the variable as a string. For strings, it will return the string "string":

<code class="js">if (typeof myVar === 'string') {
  // myVar is a string
}</code>

Instanceof Operator

The instanceof operator checks if the variable is an instance of the String object.

<code class="js">if (myVar instanceof String) {
  // myVar is a string
}</code>

Combined Approach

For more robust checking, you can combine the typeof and instanceof operators as follows:

<code class="js">if (typeof myVar === 'string' || myVar instanceof String) {
  // myVar is a string
}</code>

Additional Considerations

Note that the following values in JavaScript are considered strings:

• Empty literal string (e.g., "")
• Unicode string literals (e.g., String.fromCharCode(10000))
• Boxed strings created with the new String() constructor

However, the following values, which may appear like strings, are not considered strings:

• null
• undefined
• Objects (e.g., { a: 1, b: 2 })
• Arrays (e.g., [ 1, 2, 3 ])
• Numbers (e.g., 123)
• Zero (0)
• Regular expressions (e.g., new RegExp('hello'))
• Objects with a modified valueOf method that returns a string
• Objects that pretend to be strings by overriding the constructor property

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