JavaScript: Determine whether the current runtime environment is a browser

JavaScript fundamental (ES6 Syntax): Exercise-203 with Solution

Check Browser Environment

Write a JavaScript program to determine if the current runtime environment is a browser. This is so that front-end modules can run on the server (Node) without errors.

• Use Array.prototype.includes() on the typeof values of both window and document (globals usually only available in a browser environment unless they were explicitly defined), which will return true if one of them is undefined.
• typeof allows globals to be checked for existence without throwing a ReferenceError.
• If both of them are not undefined, then the current environment is assumed to be a browser.

Sample Solution:

JavaScript Code:

// Define a function 'isBrowser' that checks if the code is running in a browser environment
const isBrowser = () => ![typeof window, typeof document].includes('undefined');

// Test cases to check if the code is running in a browser environment
console.log(isBrowser());  
console.log(isBrowser());

Output:

true
true

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-203-1 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript program that returns true if the global window object is defined, indicating a browser environment.
• Write a JavaScript function that checks for the existence of document and navigator objects to confirm a browser.
• Write a JavaScript program that distinguishes between Node.js and browser environments using typeof window.
• Write a JavaScript function that safely accesses browser-specific objects and returns a boolean flag.

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