如何在 JavaScript 中编写内联 IF 语句？

Question

How can I use an inline if statement in JavaScript? Is there an inline else statement too?

Something like this:

var a = 2;
var b = 3;

if(a < b) {
    // do something
}

Answer 1

You don't necessarily need jQuery. JavaScript alone will do this.

var a = 2;
var b = 3;    
var c = ((a < b) ? 'minor' : 'major');

The c variable will be minor if the value is true , and major if the value is false .

---

This is known as a Conditional (ternary) Operator.

https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Operators/Conditional_Operator

Answer 2

有一个三元运算符，如下所示：

var c = (a < b) ? "a is less than b"  : "a is not less than b";

Answer 3

对于内联编写if语句，其中的代码应该只有一个语句：

if ( a < b ) // code to be executed without curly braces;

Answer 4

You can also approximate an if/else using only Logical Operators.

(a && b) || c

The above is roughly the same as saying:

a ? b : c

And of course, roughly the same as:

if ( a ) { b } else { c }

I say roughly because there is one difference with this approach, in that you have to know that the value of b will evaluate as true, otherwise you will always get c . Bascially you have to realise that the part that would appear if () { here } is now part of the condition that you place if ( here ) { } .

The above is possible due to JavaScripts behaviour of passing / returning one of the original values that formed the logical expression, which one depends on the type of operator. Certain other languages, like PHP, carry on the actual result of the operation ie true or false, meaning the result is always true or false; eg:

14 && 0          /// results as 0,  not false
14 || 0          /// results as 14, not true
1 && 2 && 3 && 4 /// results as 4,  not true
true && ''       /// results as ''
{} || '0'        /// results as {}

One main benefit, compared with a normal if statement, is that the first two methods can operate on the righthand-side of an argument ie as part of an assignment.

d = (a && b) || c;
d = a ? b : c;

if `a == true` then `d = b` else `d = c`

The only way to achieve this with a standard if statement would be to duplicate the assigment:

if ( a ) { d = b } else { d = c }

You may ask why use just Logical Operators instead of the Ternary Operator , for simple cases you probably wouldn't, unless you wanted to make sure a and b were both true. You can also achieve more streamlined complex conditions with the Logical operators, which can get quite messy using nested ternary operations... then again if you want your code to be easily readable, neither are really that intuative.

Answer 5

In plain English, the syntax explained:

if(condition){
    do_something_if_condition_is_met;
}
else{
    do_something_else_if_condition_is_not_met;
}

Can be written as:

condition ? do_something_if_condition_is_met : do_something_else_if_condition_is_not_met;

Answer 6

If you just want an inline IF (without the ELSE), you can use the logical AND operator:

(a < b) && /*your code*/;

If you need an ELSE also, use the ternary operation that the other people suggested.

Answer 7

你可以在 JavaScript 中这样做：

a < b ? passed() : failed();

Answer 8

<div id="ABLAHALAHOO">8008</div>
<div id="WABOOLAWADO">1110</div>

parseInt( $( '#ABLAHALAHOO' ).text()) > parseInt( $( '#WABOOLAWADO ).text()) ? alert( 'Eat potato' ) : alert( 'You starve' );

Answer 9

I often need to run more code per condition, by using: ( , , ) multiple code elements can execute:

var a = 2;
var b = 3;
var c = 0;

( a < b ?  ( alert('hi'), a=3, b=2, c=a*b ) : ( alert('by'), a=4, b=10, c=a/b ) );

Answer 10

FYI, you can compose conditional operators

var a = (truthy) ? 1 : (falsy) ? 2 : 3;

If your logic is sufficiently complex, then you might consider using an IIFE

var a = (function () {
  if (truthy) return 1;
  else if (falsy) return 2;
  return 3;
})();

Of course, if you plan to use this logic more than once, then you aught to encapsulate it in a function to keep things nice and DRY.

Answer 11

inline if:

(('hypothesis') ? 'truthy conclusion' : 'falsey conclusion')

truthy conclusion: statements executed when hypothesis is true

falsey conclusion: statements executed when hypothesis is false

your example:

var c = ((a < b) ? 'a<b statements' : '!(a<b) statements');

Answer 12

To add to this you can also use inline if condition with && and || operators. Like this

var a = 2;
var b = 0;

var c = (a > b || b == 0)? "do something" : "do something else";

Answer 13

Inline if in JavaScript is simple and requires no braces:

if (a < b) doSomething()

Technically you can have an else in the same line, but it requires a semicolon:

if (a < b) doSomething(); else doSomethingElse()

The above examples may not be desired by your team's coding standards. The most important thing is that you follow conventions that work for your team. Personally, I prefer if statements over ternaries in many cases because I find them easier to read.

Answer 14

Isn't the question essentially: can I write the following?

if (foo)
  console.log(bar)
else
  console.log(foo + bar)

the answer is, yes, the above will translate.

however, be wary of doing the following

if (foo)
  if (bar)
    console.log(foo)
  else 
    console.log(bar)
else 
  console.log(foobar)

be sure to wrap ambiguous code in braces as the above will throw an exception (and similar permutations will produce undesired behaviour.)

Answer 15

Simplify ternary operator

var locked = 1;
var canChange = locked != 1 ? true : false;

If the locked is 1, then the canChange variable is set to false , otherwise, it is set to true. In this case, you can simplify it by using a Boolean expression as follows:

var locked = 1;
var canChange = locked != 1;

For multiple JavaScript ternary operators The following example shows how to use two ternary operators in the same expression:

var speed = 90;
var message = speed >= 120 ? 'Too Fast' : (speed >= 80 ? 'Fast' : 'OK');
console.log(message);

It is a best practice to use the ternary operator when it makes the code easier to read. If the logic contains many if...else statements, you shouldn't use the ternary operators.

Answer 16

You can use the Ternary operator which equates to a simple if, else.

Ternary operation which calls functions for both outcomes:

(a < b) ? DoSomething() : DoSomethingElse();

Ternary operation which calls a function for only one of the outcomes:

(a < b) ? DoSomething() : {}; or (a < b)?.DoSomething();

Answer 17

(condition) ? expressionTrue : expressionFalse;

Example

int a=20, b=10;

if (a>b) {
  cout << "a greater than b";
} else {
  cout << "b greater than a";
} 

You can simply write:

int a=20, b=10;

(a>b) ? cout << "a greater than b" : cout << "b greater than a";