How does js determine that an array contains specific elements? (Method summary)

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It is a very common requirement to determine whether an array contains a specific element. There are many implementation methods in JavaScript. I have some time to summarize them today. They are sorted from strong to weak compatibility. The return type is always boolean:

Assume the array is arr and the target element is target

Loop traversal:

(arr, target) => {
  for (var i = 0; i < arr.length; i++) {
    if (arr[i] === target) {
      return true;
    }
  }
  return false;
}

Compatibility: es1

Equal algorithm: ===

indexOf:

(arr, target) => {
  return arr.indexOf(target) >= 0;
}

Compatibility: es5

Equality algorithm: ===

filter:

(arr, target) => {
  return arr.filter(el => el === target).length > 0;
}

Compatibility: es5

Equal algorithm: ===

some:

(arr, target) => {
  return arr.some(el => el === target);
}

Compatibility: es5

Equal algorithm: ===

find:

(arr, target) => {
  return arr.find(el => el === target) !== undefined;
}

Compatibility: es2015

Equal algorithm: ===

findIndex:

(arr, target) => {
  return arr.findIndex(el => el === target) >= 0;
}

Compatibility: es2015

Equal algorithm: == =

includes:

(arr, target) => {
  return arr.includes(target);
}

Compatibility: es2016

Equality algorithm: SameValueZero

==Tips:==

== The difference between = and SameValueZero is that
NaN === Nan => false and SameValueZero considers two NaNs to be equal. Please refer to MDN for details. If you want to change the implementation of === above into the implementation of SameValueZero, you can write:

el === target || (Object.is(el, NaN) && Object.is(target, NaN))

With es6 and babel so popular nowadays, most of the time we just use includes directly.

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