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Merge pull request #367 from brentguf/conditional-operators

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Conditional operators chapter
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Ilya Kantor 2018-02-06 12:51:53 +03:00 • committed by GitHub
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1-js/02-first-steps/10-ifelse/article.md
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Sometimes we need to perform different actions based on a condition. Sometimes we need to perform different actions based on a condition.
There is the `if` statement for that and also the conditional (ternary) operator for conditional evaluation which we will be referring as the “question mark” operator: `"?"` for simplicity. There is the `if` statement for that and also the conditional (ternary) operator for conditional evaluation which we will be referring as the “question mark” operator `?` for simplicity.
[cut] [cut]
## The "if" statement ## The "if" statement
The "if" statement gets a condition, evaluates it and, if the result is `true`, executes the code. The `if` statement gets a condition, evaluates it and, if the result is `true`, executes the code.
For example: For example:
@ -22,7 +22,7 @@ if (year == 2015) alert( 'You are right!' );
In the example above, the condition is a simple equality check: `year == 2015`, but it can be much more complex. In the example above, the condition is a simple equality check: `year == 2015`, but it can be much more complex.
If there is more than one command to execute, we can use a code block in figure brackets: If there is more than one statement to be executed, we have to wrap our code block inside curly braces:
```js ```js
if (year == 2015) { if (year == 2015) {
@ -31,7 +31,7 @@ if (year == 2015) {
} }
``` ```
It is recommended to use figure brackets every time with `if`, even if there is only one command. That improves readability. It is recommended to wrap your code block with curly braces `{}` every time with `if`, even if there is only one statement. That improves readability.
## Boolean conversion ## Boolean conversion
@ -128,7 +128,7 @@ alert(accessAllowed);
The so-called "ternary" or "question mark" operator lets us do that shorter and simpler. The so-called "ternary" or "question mark" operator lets us do that shorter and simpler.
The operator is represented by a question mark `"?"`. The formal term "ternary" means that the operator has three operands. It is actually the one and only operator in JavaScript which has that many. The operator is represented by a question mark `?`. The formal term "ternary" means that the operator has three operands. It is actually the one and only operator in JavaScript which has that many.
The syntax is: The syntax is:
```js ```js
@ -151,7 +151,7 @@ Technically, we can omit parentheses around `age > 18`. The question mark operat
let accessAllowed = age > 18 ? true : false; let accessAllowed = age > 18 ? true : false;
``` ```
...But parentheses make the code more readable. So it's recommended to use them. But parentheses make the code more readable, so it's recommended to use them.
````smart ````smart
In the example above it's possible to evade the question mark operator, because the comparison by itself returns `true/false`: In the example above it's possible to evade the question mark operator, because the comparison by itself returns `true/false`:
@ -164,7 +164,7 @@ let accessAllowed = age > 18;
## Multiple '?' ## Multiple '?'
A sequence of question mark `"?"` operators allows returning a value that depends on more than one condition. A sequence of question mark `?` operators allows returning a value that depends on more than one condition.
For instance: For instance:
```js run ```js run
@ -201,7 +201,7 @@ if (age < 3) {
## Non-traditional use of '?' ## Non-traditional use of '?'
Sometimes the question mark `'?'` is used as a replacement for `if`: Sometimes the question mark `?` is used as a replacement for `if`:
```js run no-beautify ```js run no-beautify
let company = prompt('Which company created JavaScript?', ''); let company = prompt('Which company created JavaScript?', '');
@ -212,7 +212,7 @@ let company = prompt('Which company created JavaScript?', '');
*/!* */!*
``` ```
Depending on the condition `company == 'Netscape'`, either the first or the second part after `"?"` gets executed and shows the alert. Depending on the condition `company == 'Netscape'`, either the first or the second part after `?` gets executed and shows the alert.
We don't assign a result to a variable here. The idea is to execute different code depending on the condition. We don't assign a result to a variable here. The idea is to execute different code depending on the condition.
@ -236,4 +236,4 @@ if (company == 'Netscape') {
Our eyes scan the code vertically. The constructs which span several lines are easier to understand than a long horizontal instruction set. Our eyes scan the code vertically. The constructs which span several lines are easier to understand than a long horizontal instruction set.
The idea of a question mark `'?'` is to return one or another value depending on the condition. Please use it for exactly that. There is `if` to execute different branches of the code. The idea of a question mark `?` is to return one or another value depending on the condition. Please use it for exactly that. There is `if` to execute different branches of the code.