How Can You Determine If a JavaScript Variable Is a Number or a String?

Determining the Nature of Variables: Numbers vs. Strings in JavaScript

When working with JavaScript variables, determining their exact nature—whether numeric or string—can be crucial for various operations. Here are some effective methods to perform this type check:

Using typeof:

This operator returns the primitive data type of a variable. For literal values, it works well:

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

Caveat with Constructors:

However, if a variable is created using a constructor (e.g., new String("foo")), typeof may return "object" due to the object wrapper in JavaScript.

Underscore.js Method:

To address this issue, the _.isString method from the popular Underscore.js library provides a more robust approach:

var toString = Object.prototype.toString;

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

This method checks for the specific string prototype and returns true even for variables created using constructors:

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

By employing these methods, you can confidently identify the true type of your variables, ensuring compatibility with various JavaScript operations and preventing unexpected errors.

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