CODEWITHSUNDEEP
javascript
cluster1
cluster1

Reputation: 5674

Existence of a method in JavaScript: Checking for truthy sufficient?

If I like to test if an object has a specific method: Would the following code work reliable?

const obj = {
  add(a, b) {
    return a + b
  }
}

if (obj.add) {
    console.log(obj.add(9, 3));
}

if (obj.sub) {
    console.log(obj.sub(8, 2));
}

Or would it potentially fail? If so: For what reason?

And if it isn't sufficient: What should I use instead?

Upvotes: 0

Views: 42

Answers (4)

Shubham Dixit
Shubham Dixit

Reputation: 1

You can try like this .Check if object key is a function, 

const obj = {
  add:function (a, b) {
    return a + b
  },
   sub:function (a, b) {
    return a - b
  }
}

if (typeof obj.add === 'function') {
    console.log(obj.add(9, 3));
}

if (typeof obj.sub === 'function') {
    console.log(obj.sub(8, 2));
}

Upvotes: 1

Snow
Snow

Reputation: 4097

Since you want to call the method, you should check to see it's actually a method first. If it's a non-function property, what you're doing will result in a TypeError.

const obj = {
  add: true
}

if (obj.add) {
    console.log(obj.add(9, 3));
}

if (obj.sub) {
    console.log(obj.sub(8, 2));
}

So:

const obj = {
  add(a, b) {
    return a + b
  },
  badProp: true
}
const verify = arg => typeof arg === 'function';
if (verify(obj.add)) {
    console.log(obj.add(9, 3));
}

if (verify(obj.sub)) {
    console.log(obj.sub(8, 2));
}

if (verify(obj.badProp)) {
    obj.badProp();
}

Upvotes: 2

Ankur
Ankur

Reputation: 516

Instead if checking for just name. I would suggest checking type too. Refer below code for same

const obj = {
  add(a, b) {
    return a + b
  }
}
if (typeof obj.add === "function") { 
    console.log(obj.add(9, 3));
}

if (typeof obj.sub === "function") {
    console.log(obj.sub(8, 2));
}

Upvotes: 1

Janie
Janie

Reputation: 646

typeof() is a way to check weather a var is a function or anything else.

if (typeof obj.add === 'function') {
    console.log(obj.add(9, 3));
}

Upvotes: 1

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