Why doe this JS array not reduce in Vuex

Question

I have a Vuex store which has a roster object. The roster object has an array of subteam objects. Each subteam object has an array of position objects. How do I count the total positions?

See the following getter:

totalPositions : function (state) {
    let reducer = (accumulator, subteam) => accumulator + subteam.positions.length;
    return state.roster.subteams.reduce(reducer);
}

When I log the result, I get something like:

"[object Object]33010600000000000000000000000000000"

The digits in the string closely resemble the actual lengths of the position arrays, but not exactly. I tried using parseInt (even though array.length should be an integer):

let reducer = (accumulator, subteam) => {
    return accumulator + parseInt(subteam.positions.length,10);
};

It didn't help.

Emile Bergeron · Accepted Answer · 2018-04-06 14:21:33Z

3

You must pass an initial value to the reduce function.

totalPositions : function (state) {
    const reducer = (accumulator, subteam) => accumulator + subteam.positions.length;
    return state.roster.subteams.reduce(reducer, 0);
}

If no initial value is supplied, the first element in the array will be used.

Since the subteam looks like an object, it is transformed into string [object Object] in the addition.

const obj = {};
console.log(obj + 13)
// => "[object Object]13"

Then say "[object Object]3" + 3 is "[object Object]33", etc. as the accumulator is now a string.

I really recommend you watch the Wat lightning talk by Gary Bernhardt from CodeMash 2012.

edited Apr 6, 2018 at 14:21

answered Apr 6, 2018 at 0:02

Emile Bergeron

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1 Comment

DatsunBing Over a year ago

You are a legend Emile.

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