为什么过滤器返回[object Object]？

Question

var persons = [
    {name : "jak" , age:20},
    {name : "hasan" , age: 15},
    {name : "reza" , age:18}
];

function adult(el,index,arr){
    if (el.age >= 18)
        return el.name;
    }

    document.getElementById("x").innerHTML = persons.filter(adult);
}

I expected jak and reza , but i see [object object] [object object].

Answer 1

The filter needs to return true to keep the element or false otherwise.

See below:

 var persons = [{ name: "jak", age: 20 }, { name: "hasan", age: 15 }, { name: "reza", age: 18 }]; function adult(el, index, arr) { if (el.age >= 18) return true; } document.getElementById("x").innerHTML = persons.filter(adult).map(function(person) { return person.name; }); 

 <div id='x'></div> 

Reference: MDN

Answer 2

You're seeing [object Object], [object Object] because you're trying to display an array of objects as a string. That's happening because you seem to think that filter creates a string based on it's return value. That's not how filter works. filter takes a function which returns true or false and creates a new array with only the results that returned true .

var adults = persons.filter(function(person) {
  return person.age >= 18;
});

If you want to map certain elements in an array to something else you can use map .

var adultNames = adults.map(function(person) {
  return person.name;
});

Finally, to convert an array into a single string, you can use join .

document.getElementById("x").innerHTML = adultNames.join('and');