JavaScript: Get the data type

Last update on February 28 2025 06:56:20 (UTC/GMT +8 hours)

JavaScript Function: Exercise-9 with Solution

Get Type of Argument

Write a JavaScript function that accepts an argument and returns the type.

Note : There are six possible values that typeof returns: object, boolean, function, number, string, and undefined.

Sample Solution-1:

JavaScript Code:

// Define a function named detect_data_type that determines the data type of the given value
function detect_data_type(value) {
  // Define an array of data types to check against: Function, RegExp, Number, String, Boolean, Object
  var dtypes = [Function, RegExp, Number, String, Boolean, Object], x, len;

  // Check if the value is an object or a function
  if (typeof value === "object" || typeof value === "function") {
    // Iterate through the array of data types
    for (x = 0, len = dtypes.length; x < len; x++) {
      // If the value is an instance of the current data type, return the data type
      if (value instanceof dtypes[x]) {
        return dtypes[x];
      }
    }
  }

  // If the value is not an object or function, return its typeof value
  return typeof value;
}

// Log the result of calling detect_data_type with the input value 12 to the console
console.log(detect_data_type(12));

// Log the result of calling detect_data_type with the input value 'w3resource' to the console
console.log(detect_data_type('w3resource'));

// Log the result of calling detect_data_type with the input value false to the console
console.log(detect_data_type(false));

Output:

number
string
boolean

Flowchart:

Live Demo:

Sample Solution-2:

JavaScript Code:

function getType(value) {
    const typeString = Object.prototype.toString.call(value);
    // Extract the type from the string, removing brackets and the "object " prefix
    return typeString.slice(8, -1).toLowerCase();
}

// Example usage:
console.log(getType("Hello")); // Output: string
console.log(getType(42));      // Output: number
console.log(getType(true));    // Output: boolean
console.log(getType(null));    // Output: null
console.log(getType(undefined));// Output: undefined
console.log(getType([]));      // Output: array
console.log(getType({}));      // Output: object

Output:

string
number
boolean
null
undefined
array
object

Flowchart:

For more Practice: Solve these Related Problems:

Write a JavaScript function that returns the type of a given argument and correctly distinguishes between null and object.
Write a JavaScript function that identifies whether an argument is an array, object, or function using both typeof and instanceof.
Write a JavaScript function that returns a string indicating the type of a variable, including support for custom class instances.
Write a JavaScript function that checks an argument’s type and throws an error if it does not match one of the expected types.

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