How do you determine if a JavaScript variable is a number or a string?

Determining Variable Type in JavaScript: Numeral or String

To ascertain the data type of a variable in JavaScript, specifically whether it's a number or a string, consider the following approaches:

Literal Notation and typeof Operator:

For variables initialized using literal notation (e.g., "Hello World" or 123), use the typeof operator:

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

Constructor Usage and typeof Operator:

When creating variables using constructors (e.g., var foo = new String("foo")), keep in mind that `typeof may return "object" for these variables.

Underscore.js Library:

For a more comprehensive method, utilize the isString method from the underscore.js library:

var toString = Object.prototype.toString;

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

This method will accurately return true for both string literals and strings created using the constructor:

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

By employing these techniques, you can effectively determine whether a JavaScript variable is a number or a string, regardless of its initialization method.

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