TypeScript and array reduce function

Do you know what the reduce array method does in TypeScript? Can you provide a simple example of usage?

I searched on Google and the TypeScript language specification but could not find any decent explanation and examples.

Solution 1:

Just a note in addition to the other answers.

If an initial value is supplied to reduce then sometimes its type must be specified, viz:-

a.reduce(fn, [])

may have to be

a.reduce<string[]>(fn, [])

or

a.reduce(fn, <string[]>[])

Solution 2:

It's actually the JavaScript array reduce function rather than being something specific to TypeScript.

As described in the docs: Apply a function against an accumulator and each value of the array (from left-to-right) as to reduce it to a single value.

Here's an example which sums up the values of an array:

let total = [0, 1, 2, 3].reduce((accumulator, currentValue) => accumulator + currentValue);
console.log(total);

The snippet should produce 6.

Solution 3:

With TypeScript generics you can do something like this.

class Person {
    constructor (public Name : string, public Age: number) {}
}

var list = new Array<Person>();
list.push(new Person("Baby", 1));
list.push(new Person("Toddler", 2));
list.push(new Person("Teen", 14));
list.push(new Person("Adult", 25));

var oldest_person = list.reduce( (a, b) => a.Age > b.Age ? a : b );
alert(oldest_person.Name);

Solution 4:

Reduce() is..

• The reduce() method reduces the array to a single value.
• The reduce() method executes a provided function for each value of the array (from left-to-right).
• The return value of the function is stored in an accumulator (result/total).

It was ..

let array=[1,2,3];
function sum(acc,val){ return acc+val;} // => can change to (acc,val)=>acc+val
let answer= array.reduce(sum); // answer is 6

Change to

let array=[1,2,3];
let answer=arrays.reduce((acc,val)=>acc+val);

Also you can use in

1. find max

    let array=[5,4,19,2,7];
    function findMax(acc,val)
    {
     if(val>acc){
       acc=val; 
     }
    }

    let biggest=arrays.reduce(findMax); // 19

2. find an element that not repeated.

    arr = [1, 2, 5, 4, 6, 8, 9, 2, 1, 4, 5, 8, 9]
    v = 0
    for i in range(len(arr)):
    v = v ^ arr[i]
    print(value)  //6