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

Identifying Variable Type: Number vs. String in JavaScript

Determining whether a variable in JavaScript represents a number or a string can be crucial for various operations. In this article, we explore multiple methods to effectively check variable types.

Using typeof Operator

For literal values, the typeof operator provides a basic way to distinguish between numbers and strings. It returns "string" for string literals and "number" for numeric literals.

typeof "Hello World"; // string
typeof 123;           // number

Handling Constructed Variables

When dealing with variables created using constructors (e.g., var foo = new String("foo")), the typeof operator may return "object." To address this, consider the following approach:

var toString = Object.prototype.toString;

function isString(obj) {
  return toString.call(obj) == '[object String]';
}

console.log(isString("Jonathan")); // true
console.log(isString(new String("Jonathan"))); // true

This method leverages the toString method of the Object prototype to determine the object type. It returns a boolean value, indicating whether or not the variable is a string.

By employing these techniques, you can reliably check the type of JavaScript variables and ensure correct data handling in your code.

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