f09e84ff14
Added curly brackets where they had been left out of the code snippets. Also fixed two grammatical errors on line 52
98 lines
2.2 KiB
Markdown
98 lines
2.2 KiB
Markdown
---
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title: If-Else Statement
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---
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## Introduction
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The `if` statement executes a statement if a specified condition is `true`. If the condition is `false`, another statement can be executed using the `else` statement.
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**Note:** The `else` statement is optional.
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```javascript
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if (condition) {
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/* do something */
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} else {
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/* do something else */
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}
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```
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Multiple `if...else` statements can be chained to create an `else if` clause. This specifies a new condition to test and can be repeated to test multiple conditions, checking until a true statement is presented to execute.
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```javascript
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if (condition1) {
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/* do something */
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} else if (condition2) {
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/* do something else */
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} else if (condition3) {
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/* do something else */
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} else {
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/* final statement */
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}
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```
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**Note:** If you want to execute more than one statement in the `if`, `else` or `else if` part, curly braces are required around the statements:
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```javascript
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if (condition) {
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/* do */
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/* something */
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/* with multiple statements */
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} else {
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/* do something */
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/* else */
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}
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```
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<a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/if...else' target='_blank' rel='nofollow'>MDN link</a> | <a href='https://msdn.microsoft.com/en-us/library/85yyde5c.aspx' target='_blank' rel='nofollow'>MSDN link</a>
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### Additional ternary operator
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For a simple operation like assigning a value to a variable conditionally you can use a ternary operator, which is a shorthand syntax for an `if...else` clause in JavaScript
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```javascript
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// Normal if...else
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let num = 1;
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if (someCondition){
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num = 1;
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} else {
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num = 0;
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}
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// Using ternary operator
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const num = someCondition ? 1 : 2;
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// condition ? true case : false case
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```
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## Examples
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**Using** `if...else`:
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```javascript
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// If x = 5, then z = 7 and q = 42.
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// If x is not 5, then z = 19.
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if (x == 5) {
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z = 7;
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q = 42
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} else {
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z = 19;
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}
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```
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**Using** `else if`:
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```javascript
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if (x < 10) {
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return "Small number";
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} else if (x < 50) {
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return "Medium number";
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} else if (x < 100) {
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return "Large number";
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} else {
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flag = 1;
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return "Invalid number";
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}
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```
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**Using** `if` **alone**:
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```javascript
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// This function can also act as a Boolean
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if (x < 30) {
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return "true";
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}
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