Day 3: The find helper
The find helper loops through an array to look for a particular element (first occurrence), which passes the given criteria.
It runs the provided function over each element, and if the particular element passes the criteria, it is returned. If no element found, undefined is returned.
This helper method does not change the original array.
The Drawback
The find helper will not work when you want to find more than one occurrences, it will work only when you need the first occurrence.
Which element to choose?
In the find helper we pass an iterator function which iterates over all the elements of the array. The function should have a condition, and the first element which satisfies that condition is returned.
When the condition is passed, the iterator function must return true. The element at which the iterator function returns a true is taken to be the required element.
Example 1
Given an array of numbers, find the first element which is a multiple of 7
/**
* Given an array of numbers,
* find the first element which is a multiple of 7
*/
const numbers = [1, 13, 15, 18, 28, 32, 47, 50];
let firstMultiple;
// Without the `find` helper
for (let i=0; i<numbers.length; i++) {
if (numbers[i]%7 === 0) {
firstMultiple = numbers[i];
break;
}
}
console.log (firstMultiple);
// With `find` helper (without arrow func)
let firstMultiple2 = numbers.find (function (number) {
if (number%7 === 0) {
return true;
}
});
console.log (firstMultiple2);
// With `find` helper (with arrow func)
let firstMultiple3 = numbers.find (number => number%7 === 0);
console.log (firstMultiple3);
Example 2
Given an array of objects having the data of students, find the student having register number 9018
const students = [
{ regNo: 0192, name: "Madhav" },
{ regNo: 1302, name: "Ram" },
{ regNo: 6723, name: "Rahul" },
{ regNo: 9018, name: "John" },
{ regNo: 4211, name: "Taylor" },
];
let wantedStudent = students.find (student => student.regNo === 9018);
console.log (wantedStudent);
Syntax
array.find(function(currentValue, index, arr),thisValue)
- currentValue: Required. The value of the current element
- index: Optional. The array index of the current element
- arr: Optional. The array object the current element belongs to
- thisValue: Optional. A value to be passed to the function to be used as its “this” value
Practice Questions
To be added..
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