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javascript-xxx is not a function

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Symbols count in article: 90 Reading time ≈ 1 mins.

Have you ever seen this error: “TypeError: xxx is not a function”? This error occurs when you try to call a function that does not exist.

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const person = {
  name: 'Philip',
  age: 18,
};

person.getAge(); // TypeError: person.getAge is not a function

You can solve this by the optional chaining operator ?.:

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person.getAge?.(); // nothing output

However, if there is a property in the object has the same name by accident, you will still get that error

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const person = {
  name: 'Philip',
  age: 18,
  getAge: 18,
};

person.getAge?.(); // TypeError: person.getAge is not a function