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Q&A Explaining the result of an arithmetic expression in JavaScript

I misunderstand why the following code outputs -1 in console. x = 42; x = (x == 42) * -1 + (x != 42) * x; -1 Due to Type Coercion, the comparison of x to 42 yields true and is thus transl...

2 answers  ·  posted 2y ago by deleted user  ·  edited 2y ago by Alexei‭

#4: Post edited by user avatar Alexei‭ · 2022-05-01T17:11:46Z (over 2 years ago)
Replaced the title to match what is actually being asked
  • Type coercion with both true and false in JavaScript
  • Explaining the result of an arithmetic expression in JavaScript
#3: Post edited by user avatar Dirk Herrmann‭ · 2022-05-01T14:47:51Z (over 2 years ago)
The question is about operator precendence rather than type coercion. I was thinking also about changing the title in this direction...
Type coercion with both true and false in JavaScript
I misunderstand why the following code outputs -1 in console.

```javascript
x = 42;
x = (x == 42) * -1 + (x != 42) * x;
```

> -1

Due to [Type Coercion](https://developer.mozilla.org/en-US/docs/Glossary/Type_coercion), the comparison of x to 42 yields `true` and is thus translated to `1`.

So `1 * -1` yields `-1`.

Now, `(x != 42)` which is `false` yields `0` so I have expected to get in console

> -42

Because `-1 + 0 * 42 MEANS -42`.

So why did I get `-1` in the end?
#2: Post edited by (deleted user) · 2022-04-30T21:51:43Z (over 2 years ago)
  • I misunderstand why the following code outputs -1 in console.
  • ```javascript
  • x = 42;
  • x = (x == 42) * -1 + (x != 42) * x;
  • ```
  • > -1
  • Due to [Type Coercion](https://developer.mozilla.org/en-US/docs/Glossary/Type_coercion), the comparison of x to 42 yields `true` and is thus translated to `1`.
  • So `1 * -1` yields `-1`.
  • Now, to `(x != 42)` which is `false` yields `0` so I have expected to get in console
  • > -42
  • Because `-1 + 0 * 42 MEANS -42`.
  • So why did I get `-1` in the end?
  • I misunderstand why the following code outputs -1 in console.
  • ```javascript
  • x = 42;
  • x = (x == 42) * -1 + (x != 42) * x;
  • ```
  • > -1
  • Due to [Type Coercion](https://developer.mozilla.org/en-US/docs/Glossary/Type_coercion), the comparison of x to 42 yields `true` and is thus translated to `1`.
  • So `1 * -1` yields `-1`.
  • Now, `(x != 42)` which is `false` yields `0` so I have expected to get in console
  • > -42
  • Because `-1 + 0 * 42 MEANS -42`.
  • So why did I get `-1` in the end?
#1: Initial revision by (deleted user) · 2022-04-30T20:20:36Z (over 2 years ago)
Type coercion with both true and false in JavaScript
I misunderstand why the following code outputs -1 in console.

```javascript
x = 42;
x = (x == 42) * -1 + (x != 42) * x;
```

> -1

Due to [Type Coercion](https://developer.mozilla.org/en-US/docs/Glossary/Type_coercion), the comparison of x to 42 yields `true` and is thus translated to `1`.

So `1 * -1` yields `-1`.

Now, to `(x != 42)` which is `false` yields `0` so I have expected to get in console

> -42

Because `-1 + 0 * 42 MEANS -42`.

So why did I get `-1` in the end?