Find.md

find() method

The find() method in JavaScript returns the first element in the array that satisfies the provided testing function. If no values satisfy the testing function, undefined is returned.

Here's how it works:

1. It tests each item in the array against a condition defined in a function.
2. The provided function is called with three arguments: the current element, the index of the current element, and the array find() was called upon.
3. It returns the first element that satisfies the condition. If no elements satisfy the condition, it returns undefined.
4. It does not mutate the original array.

Here's a simple example:

const numbers = [1, 2, 3, 4, 5];

const found = numbers.find(function(number) {
    return number > 3;
});

console.log(found); // Output: 4

In this example, find() is called on the numbers array and returns the first number that is greater than 3.

Syntax

The syntax for the find() method in JavaScript is as follows:

array.find(callbackFunc(currentValue, index, arr), thisValue)

Here's what each parameter means:

• callbackFunc(currentValue, index, arr): A function to be called for each element in the array. This function accepts three arguments:
  • currentValue: The current element being processed in the array.
  • index (optional): The index of the current element being processed in the array.
  • arr (optional): The array find was called upon.
• thisValue (optional): A value to use as this when executing the callback function.

The find() method returns the value of the first element in the array that satisfies the provided testing function. Otherwise undefined is returned.

Polyfill

const numbers = [1, 2, 3, 4, 5];

Array.prototype.find = function(callbackFunc){
    if (this == null) {
      throw new TypeError('Array.prototype.find called on null or undefined');
    }
    if (typeof callbackFunc !== 'function') {
      throw new TypeError('callback must be a function');
    }
    for (let i = 0; i < this.length; i++) {
      if (callbackFunc(this[i], i, this)) {
        return this[i];
      }
    }
    return undefined;
}

console.log(numbers.find(found)) //  Output: 4