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The JavaScript Interview Handbook: 100+ Interview Questions

Solution Review: Array or Not?

Explore how to identify whether a variable is an array in JavaScript by using Object.prototype.toString with call to check the internal [[Class]] of the object. Understand why this method works reliably and how type detection relates to prototypes and inheritance.

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Solution

Javascript (babel-node)
function check(obj) {
  if (Object.prototype.toString.call(obj) === "[object Array]") {
    return true;
  } else {
    return false;
  }
}
console.log(check(123));
console.log(check("cat"));
console.log(check([1, 2, 3, 4]));

Explanation

To check whether the passed in object is an array or ...