Checking the Type of a Variable in JavaScript: Number vs. String

In JavaScript, determining the type of a variable is crucial for successful data manipulation. This article provides practical solutions to check whether a variable represents a number or a string.

Using the typeof Operator

If the variable holds a literal value (e.g., "Hello World" or 123), the typeof operator can be utilized as follows:

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

Handling Constructor-Generated Variables

When variables are created using constructors (e.g., new String("foo")), typeof may return "object" instead of the expected "string". To overcome this, a more robust approach is to use a method found in underscore.js:

var toString = Object.prototype.toString;

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

This method accurately returns true for both literal strings and string objects generated via constructors:

_.isString("Jonathan"); // true
_.isString(new String("Jonathan")); // true

By employing either of these methods, developers can confidently determine the type of a variable, ensuring the proper handling and manipulation of data in JavaScript applications.