如何在函数中编写if / else语句，该函数告诉我数字是否可以被2整除（在javascript中）

Question

I'm working through codacademy and I can't understand the help discussions in the forum.

This is what I have so far but it returns false when i run the function with an even number:

var isEven = function(number) {
 if (isEven % 2 == 0){
  return true;
 }else{
  return false;
 }
};

Answer 1

You are performing the mathematical operation on isEven (the function itself). You need to check number :

var isEven = function(number) {
    if (number % 2 === 0) {
        return true;
    } else {
        return false;
    }
};

or better yet:

var isEven = function(number) {
    return number % 2 === 0;
};

You could even do this, by making use of the truthy/falsy behavior of 1 and 0 :

var isEven = function(number) {
    return !(number % 2);
};

but I think the previous approach more clearly conveys how the logic works.

Answer 2

you can write this function as follows:

var isEven = function(number) {
 return ((number % 2) == 0);
}

Answer 3

Your function is not working because you're checking against the function name, not the function parameter (number). Try this:

var isEven = function(number) {
    return number % 2 == 0;
}

Answer 4

You doing it wrong in isEven itself.. Do it like..

var isEven = function(number) {
    return number% 2 == 0;
}

Answer 5

Consider the following:

• 0 is considered to be false in Javascript.
• 1 is considered to be true in Javascript.
• ! makes false become true and vice versa.
• The % operator can be used to keep higher numbers in a zero-to-one range.

Since 0 % 2 gives 0 (ie false ) and 1 % 2 gives 1 (ie true ), you simply need to invert the result with ! :

function isEven(x) { return !(x % 2); }

console.log(isEven(0));  // true
console.log(isEven(1));  // false
console.log(isEven(2));  // true
console.log(isEven(3));  // false

Note that this could also be written as:

function isEven(x) { return (x % 2) == 0; }

...because:

• 0 % 2 is 0 (so it is true to say that it is equal to zero).
• 1 % 2 is 1 (so it is false to say that it is equal to zero).