Why does this programme return false?

Language Help JavaScript
1 
let earlyReg = false;

let runnerAge = 20;

const earlyAndOld = earlyReg = true && runnerAge > 18;

const old = earlyReg = false && runnerAge > 18;

const young = runnerAge < 18;

console.log(old)
2

What is your expected outcome from that statement?

Hint:

false && 'anything' will always yield, false.

2 Likes
3

Well my hope was that since the first variable was false, the statement that evaluated if that statement was false would come out true, since i told it to see if something was false…
If that makes sense? If you need a better explanation i can try to offer it?

4

False will short-circuit AND so will always be false. We cannot AND false and expect anything different.

Also, it is pointless to compare to a boolean. Use truthiness, instead.

earlyReg && runnerAge > 18
2 Likes
5

But then how do i make it so that something happens if earlyreg is false?

6

Describe the problem, or post a link to the exercise so we can read what is instructed.

1 Like
7

What do you want to happen if earlyReg is false?

1 Like
8

well basically i just want it to log stuff to the console.

codecademy.com/projects/practice/race-day

9

The = operator is used for assignment. For comparisons, you should use the equality operator ==.

// You wrote:
const earlyAndOld = earlyReg = true && runnerAge > 18;

// It should be:
const earlyAndOld = (earlyReg == true) && (runnerAge > 18);

However, as mtf pointed out, when comparing with booleans, it is better to use truthiness i.e.

// Instead of:
const earlyAndOld = (earlyReg == true) && (runnerAge > 18);
// better to use:
const earlyAndOld = (earlyReg) && (runnerAge > 18);

// Instead of:
const old = (earlyReg == false) && (runnerAge > 18);
// better to use:
const old = (!earlyReg) && (runnerAge > 18);

I have used parentheses for clarity. If you prefer, you can omit them.

If you use assignment operator instead of comparison, then

let flag = false;

if (flag = true) {
    console.log("Condition met!");
}

console.log(flag);

// Output:
"Condition met!"
true

// The assignment operator assigned true to the flag variable.

as opposed to comparison operator:

let flag = false;

// Using (flag == true) just as an example. 
// if (flag) { ... would be better.

if (flag == true) {     
    console.log("Condition met!");
}

console.log(flag);

// Output:
false
1 Like
10

i’m a little unclear here? it seems to have become true without being specifically changed?

11 
let flag = false;

if (flag = true) {
    console.log("Condition met!");
}

console.log(flag);

// Output:
"Condition met!"
true

If you use the assignment operator =, then you are specifically changing the value assigned to the variable.
Even though the assignment operator is being used in the condition, the assignment is still made.

if (flag = true) { ...

Here is a sketch of how the above will be evaluated:

  • First, the expression within the parentheses will be evaluated (so that the decision to execute or skip the if block can be made).

  • Since the assignment operator = has been used (instead of the comparison operator ==), so the boolean value true will be assigned to the flag variable. Whatever value had been previously assigned to flag would be over-written.

  • After the assignment has been made, the expression if (flag = true) { is equivalent to if (flag) {. Since flag is truthy, so the expression evaluates to true and the if block is executed.

When making comparisons, don’t use the assignment operator =
Instead use the equality comparison operator ==

1 Like
12

ah, thank you! i always thought it only assigned things if flag=true was on it’s own.

1 Like
14

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