预期在箭头函数结束时返回一个值：array-callback-return

Question

I have a couple of actions on a function to extract unix time at midnight, I map through the array and then filter by those values that modulus to 0. However I keep getting this pesky error msg, regardless of whether I return the map function or not.. Code below:

  midnightFunction = arr => {
    return arr.map(v =>
      v.filter(t => {
        if (t.published_at % 86400 === 0) {
          return t;
        };
      }
      )
    );
  };

My array is an array and looks like this:

[[{published_at: 1578960000, value: 20.41}, {published_at: 1578960000, value: 20.41},...etc ], [], []...], [[], [], []...] , ... etc

I want the result to have the same structure, but return just those values that match the condition.

t.published_at % 86400 === 0

Answer 1

The function you pass to array.filter() should always return a truthy or falsy value. In your current code, if t.published_at % 86400 is not zero, the function doesn't return any value (it returns undefined). Additionally, if that value is zero, instead of returning something like true/false it returns the element itself.

Your function should be as simple as this:

 const midnightFunction = arr => arr.map(v => v.filter(t => t.published_at % 86400 === 0)); //for demonstration let data = [[{published_at: 1578960000, value: 20.41}, {published_at: 1578970000, value: 23.21}],[{published_at: 1578873601, value: 14.01}, {published_at: 1578873600, value: 27.25}]]; console.log(midnightFunction(data));