Henry Zhu Henry Zhu - 1 month ago 26
Javascript Question

How to use ES6 Fat Arrow to .filter() an array of objects

I'm trying to use ES6 arrow function with

.filter
to return adults (Jack & Jill). It appears I cannot use an if statement.

What do I need to know in order to do this in ES6?

var family = [{"name":"Jack", "age": 26},
{"name":"Jill", "age": 22},
{"name":"James", "age": 5 },
{"name":"Jenny", "age": 2 }];

let adults = family.filter(person => if (person.age > 18) person); // throws error

(8:37) SyntaxError: unknown: Unexpected token (8:37)
|let adults = family.filter(person => if (person.age > 18) person);


My working ES5 example:

let adults2 = family.filter(function (person) {
if (person.age > 18) { return person; }
});

Answer

It appears I cannot use an if statement.

Arrow functions either allow to use an expression or a block as their body. Passing an expression

foo => bar

is equivalent to the following block

foo => { return bar; }

However,

if (person.age > 18) person

is not an expression, if is a statement. Hence you would have to use a block, if you wanted to use if in an arrow function:

foo => {  if (person.age > 18) return person; }

While that technically solves the problem, this a confusing use of .filter, because it suggests that you have to return the value that should be contained in the output array. However, the callback passed to .filter should return a Boolean, i.e. true or false, indicating whether the element should be included in the new array or not.

So all you need is

family.filter(person => person.age > 18);

In ES5:

family.filter(function (person) {
  return person.age > 18;
});
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