Use array.reduce() for array of characters

Question

I have an array of characters (arr) and a string (J), I wanted to use the array.reduce() method to count the number of characters of the array (arr) present in the string J.

Below is the code which shows how I am using array.reduce() method,

let val = arr.reduce((count , ch) => {
    return J.includes(ch) ? count + 1 : count
});

But when I tried with sample value as,

arr = [ 'a', 'A', 'A', 'S', 'S' ];

J = 'aA';

I get the anser as

val = 'a11'

Mohammad · Accepted Answer · 2018-11-18 10:02:01Z

6

You need to add initialValue in second parameter of .reduce() as mentioned in docs

arr.reduce(callback[, initialValue])

var arr = [ 'a', 'A', 'A', 'S', 'S' ];
var J = 'aA';
let val = arr.reduce((count , ch) => {
    return J.includes(ch) ? count + 1 : count
}, 0);
console.log(val);

edited Nov 18, 2018 at 10:02

answered Nov 18, 2018 at 9:56

Mohammad

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