Can you explain how `var in array` differs from using `array.indexOf(var)`?

Question

Can you explain how `var in array` differs from using `array.indexOf(var)`?

Currently, I am delving into the world of arrays in JavaScript. My main inquiry revolves around determining the equivalence of the two tests below:

var test = 2;
console.log(test in [1,2,3]);
console.log([1,2,3].indexOf(test) != -1);

Initially, these tests appear to yield similar results. However, after coming across responses on platforms like this and insights from the book I am currently engrossed in, doubts have arisen. It is argued that using the in operator with an array is not supported, but rather intended for objects. This discrepancy prompts the question: why do individuals opt for .indexOf(x), presumed to be linear time, over in, assumed to offer constant time efficiency?

javascript arrays

Answer 1

Answer №1

Nope. They are actually quite distinct.

examining in [1,2,3] verifies if there exists a trait known as 2 within the entity. Indeed, it does; possessing the value 3.

[1,2,3].locationOf(examining) retrieves the first characteristic with the numerical representation 2 (situated within the attribute labeled as 1)

suggest that conducting this operation is impossible on an array, solely achievable on an object

It's worthy to note that arrays are essentially type of objects. (A specialized form if we adhere to conventional OO terminology, while not precisely suitable for a prototypal language like JS, but serves its purpose).

The set [1, 2, 3] somewhat resembles an instance of an object { "0": 1, "1": 2, "2": 3 } (still, inheriting several other aspects from the Array constructor).

Answer 2

Nope. They are actually quite distinct.

examining in [1,2,3] verifies if there exists a trait known as 2 within the entity. Indeed, it does; possessing the value 3.

[1,2,3].locationOf(examining) retrieves the first characteristic with the numerical representation 2 (situated within the attribute labeled as 1)

suggest that conducting this operation is impossible on an array, solely achievable on an object

It's worthy to note that arrays are essentially type of objects. (A specialized form if we adhere to conventional OO terminology, while not precisely suitable for a prototypal language like JS, but serves its purpose).

The set [1, 2, 3] somewhat resembles an instance of an object { "0": 1, "1": 2, "2": 3 } (still, inheriting several other aspects from the Array constructor).

Answer 3

Answer №2

According to information from MDN website,

The in operator will return true if the specified property exists within the specified object.

in is used to check for keys, similar to using Object.keys(array).indexOf(test)

var a1 = [1,2,3];
var a2 = ['a', 'b', 'c']
var test = 2;

console.log(test in a1)
console.log(test in a2)

// Best practice

//ES5
console.log(a1.indexOf(test)>-1)
console.log(a2.indexOf(test)>-1)

//ES6
console.log(a1.includes(test))
console.log(a2.includes(test))

Answer 4

According to information from MDN website,

The in operator will return true if the specified property exists within the specified object.

in is used to check for keys, similar to using Object.keys(array).indexOf(test)

var a1 = [1,2,3];
var a2 = ['a', 'b', 'c']
var test = 2;

console.log(test in a1)
console.log(test in a2)

// Best practice

//ES5
console.log(a1.indexOf(test)>-1)
console.log(a2.indexOf(test)>-1)

//ES6
console.log(a1.includes(test))
console.log(a2.includes(test))

Answer 5

Answer №3

When checking for an index or if a property of an object exists, the first code snippet does this by:

console.log(test in [1,2,3]);

It is important to note that this code does not check for a specific value within the array like the second code snippet does:

console.log([1,2,3].indexOf(test) != -1);

Answer 6

When checking for an index or if a property of an object exists, the first code snippet does this by:

console.log(test in [1,2,3]);

It is important to note that this code does not check for a specific value within the array like the second code snippet does:

console.log([1,2,3].indexOf(test) != -1);

Answer 7

Answer №4

The in operator determines whether a specified property exists within a given object.

When using the in operator with an array, it checks for the presence of the indices and the length property - as these are the properties specific to arrays:

console.log(Object.getOwnPropertyNames([1, 2, 3]));
console.log(Object.keys([1, 2, 3]));
console.log('length' in [1, 2, 3]);

Object.keys : returns all enumerable properties

Object.getOwnPropertyNames : returns all properties

Answer 8

The in operator determines whether a specified property exists within a given object.

When using the in operator with an array, it checks for the presence of the indices and the length property - as these are the properties specific to arrays:

console.log(Object.getOwnPropertyNames([1, 2, 3]));
console.log(Object.keys([1, 2, 3]));
console.log('length' in [1, 2, 3]);

Object.keys : returns all enumerable properties

Object.getOwnPropertyNames : returns all properties

Answer 9

Answer №5

Give this a shot

let value = 2;
let arrayValue = [1, 5, 2, 4];
let result = arrayValue.indexOf(value);
if(result > -1) {
    console.log("Found it");
} else {
    console.log("Not Found");
}

Answer 10

Give this a shot

let value = 2;
let arrayValue = [1, 5, 2, 4];
let result = arrayValue.indexOf(value);
if(result > -1) {
    console.log("Found it");
} else {
    console.log("Not Found");
}

Can you explain how `var in array` differs from using `array.indexOf(var)`?

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

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