Related
In JavaScript you can use ++ operator before (pre-increment) or after the variable name (post-increment). What, if any, are the differences between these ways of incrementing a variable?
Same as in other languages:
++x (pre-increment) means "increment the variable; the value of the expression is the final value"
x++ (post-increment) means "remember the original value, then increment the variable; the value of the expression is the original value"
Now when used as a standalone statement, they mean the same thing:
x++;
++x;
The difference comes when you use the value of the expression elsewhere. For example:
x = 0;
y = array[x++]; // This will get array[0]
x = 0;
y = array[++x]; // This will get array[1]
++x increments the value, then evaluates and stores it.
x++ evaluates the value, then increments and stores it.
var n = 0, m = 0;
alert(n++); /* Shows 0, then stores n = 1 */
alert(++m); /* Shows 1, then stores m = 1 */
Note that there are slight performance benefits to using ++x where possible, because you read the variable, modify it, then evaluate and store it. Versus the x++ operator where you read the value, evaluate it, modify it, then store it.
As I understand them if you use them standalone they do the same thing. If you try to output the result of them as an expression then they may differ. Try alert(i++) as compared to alert(++i) to see the difference. i++ evaluates to i before the addition and ++i does the addition before evaluating.
See http://jsfiddle.net/xaDC4/ for an example.
I've an explanation of understanding post-increment and pre-increment. So I'm putting it here.
Lets assign 0 to x
let x = 0;
Lets start with post-increment
console.log(x++); // Outputs 0
Why?
Lets break the x++ expression down
x = x;
x = x + 1;
First statement returns the value of x which is 0
And later when you use x variable anywhere, then the second statement is executed
Second statement returns the value of this x + 1 expression which is (0 + 1) = 1
Keep in mind the value of x at this state which is 1
Now lets start with pre-increment
console.log(++x); // Outputs 2
Why?
Lets break the ++x expression down
x = x + 1;
x = x;
First statement returns the value of this x + 1 expression which is (1 + 1) = 2
Second statement returns the value of x which is 2 so x = 2 thus it returns 2
Hope this would help you understand what post-increment and pre-increment are!
var a = 1;
var b = ++a;
alert('a:' + a + ';b:' + b); //a:2;b:2
var c = 1;
var d = c++;
alert('c:' + c + ';d:' + d); //c:2;d:1
jsfiddle
var x = 0, y = 0;
//post-increment: i++ returns value then adds one to it
console.log('x++ will log: ', x++); //0
console.log('x after x++ : ', x); //1
//pre-increment: adds one to the value, then returns it
console.log('++y will log: ', ++y); //1
console.log('y after ++y : ', y); //1
It is clearer and faster to use ++i if possible :
++i guarantees that you are using a value of i that will remains the same unless you change i
i++ allows to use a value of i which will change in the "near future", it is not desirable if possible
Of course, it's not really much faster, only a little.
Good afternoon, please explain why, when waiting for 3, 4 is output to the console.
let x = 1;
console.log (x++ + ++x) // 4
At first, I thought that the priority of operations, but then why in such an example outputs 8, and not 6 for example?
let x = 1;
console.log (x++ + ++x + ++x) // 8
Sorry, if this question is duplicated, but I can't find any about this question.
For the first example:
let x = 1;
console.log (x++ + ++x) // 4
x++ returns the value of x (1) and increments it afterward. x is now 2. (This is postfix increment.)
++x increments the value of x and returns it, which is 3 (2 + 1). (This is prefix increment.)
1 + 3 = 4
See Increment Operator.
x++ or x-- is first use then update.
++x or --x is first update then use.
update means update the value of the variable x.
In JavaScript you can use ++ operator before (pre-increment) or after the variable name (post-increment). What, if any, are the differences between these ways of incrementing a variable?
Same as in other languages:
++x (pre-increment) means "increment the variable; the value of the expression is the final value"
x++ (post-increment) means "remember the original value, then increment the variable; the value of the expression is the original value"
Now when used as a standalone statement, they mean the same thing:
x++;
++x;
The difference comes when you use the value of the expression elsewhere. For example:
x = 0;
y = array[x++]; // This will get array[0]
x = 0;
y = array[++x]; // This will get array[1]
++x increments the value, then evaluates and stores it.
x++ evaluates the value, then increments and stores it.
var n = 0, m = 0;
alert(n++); /* Shows 0, then stores n = 1 */
alert(++m); /* Shows 1, then stores m = 1 */
Note that there are slight performance benefits to using ++x where possible, because you read the variable, modify it, then evaluate and store it. Versus the x++ operator where you read the value, evaluate it, modify it, then store it.
As I understand them if you use them standalone they do the same thing. If you try to output the result of them as an expression then they may differ. Try alert(i++) as compared to alert(++i) to see the difference. i++ evaluates to i before the addition and ++i does the addition before evaluating.
See http://jsfiddle.net/xaDC4/ for an example.
I've an explanation of understanding post-increment and pre-increment. So I'm putting it here.
Lets assign 0 to x
let x = 0;
Lets start with post-increment
console.log(x++); // Outputs 0
Why?
Lets break the x++ expression down
x = x;
x = x + 1;
First statement returns the value of x which is 0
And later when you use x variable anywhere, then the second statement is executed
Second statement returns the value of this x + 1 expression which is (0 + 1) = 1
Keep in mind the value of x at this state which is 1
Now lets start with pre-increment
console.log(++x); // Outputs 2
Why?
Lets break the ++x expression down
x = x + 1;
x = x;
First statement returns the value of this x + 1 expression which is (1 + 1) = 2
Second statement returns the value of x which is 2 so x = 2 thus it returns 2
Hope this would help you understand what post-increment and pre-increment are!
var a = 1;
var b = ++a;
alert('a:' + a + ';b:' + b); //a:2;b:2
var c = 1;
var d = c++;
alert('c:' + c + ';d:' + d); //c:2;d:1
jsfiddle
var x = 0, y = 0;
//post-increment: i++ returns value then adds one to it
console.log('x++ will log: ', x++); //0
console.log('x after x++ : ', x); //1
//pre-increment: adds one to the value, then returns it
console.log('++y will log: ', ++y); //1
console.log('y after ++y : ', y); //1
It is clearer and faster to use ++i if possible :
++i guarantees that you are using a value of i that will remains the same unless you change i
i++ allows to use a value of i which will change in the "near future", it is not desirable if possible
Of course, it's not really much faster, only a little.
In JavaScript you can use ++ operator before (pre-increment) or after the variable name (post-increment). What, if any, are the differences between these ways of incrementing a variable?
Same as in other languages:
++x (pre-increment) means "increment the variable; the value of the expression is the final value"
x++ (post-increment) means "remember the original value, then increment the variable; the value of the expression is the original value"
Now when used as a standalone statement, they mean the same thing:
x++;
++x;
The difference comes when you use the value of the expression elsewhere. For example:
x = 0;
y = array[x++]; // This will get array[0]
x = 0;
y = array[++x]; // This will get array[1]
++x increments the value, then evaluates and stores it.
x++ evaluates the value, then increments and stores it.
var n = 0, m = 0;
alert(n++); /* Shows 0, then stores n = 1 */
alert(++m); /* Shows 1, then stores m = 1 */
Note that there are slight performance benefits to using ++x where possible, because you read the variable, modify it, then evaluate and store it. Versus the x++ operator where you read the value, evaluate it, modify it, then store it.
As I understand them if you use them standalone they do the same thing. If you try to output the result of them as an expression then they may differ. Try alert(i++) as compared to alert(++i) to see the difference. i++ evaluates to i before the addition and ++i does the addition before evaluating.
See http://jsfiddle.net/xaDC4/ for an example.
I've an explanation of understanding post-increment and pre-increment. So I'm putting it here.
Lets assign 0 to x
let x = 0;
Lets start with post-increment
console.log(x++); // Outputs 0
Why?
Lets break the x++ expression down
x = x;
x = x + 1;
First statement returns the value of x which is 0
And later when you use x variable anywhere, then the second statement is executed
Second statement returns the value of this x + 1 expression which is (0 + 1) = 1
Keep in mind the value of x at this state which is 1
Now lets start with pre-increment
console.log(++x); // Outputs 2
Why?
Lets break the ++x expression down
x = x + 1;
x = x;
First statement returns the value of this x + 1 expression which is (1 + 1) = 2
Second statement returns the value of x which is 2 so x = 2 thus it returns 2
Hope this would help you understand what post-increment and pre-increment are!
var a = 1;
var b = ++a;
alert('a:' + a + ';b:' + b); //a:2;b:2
var c = 1;
var d = c++;
alert('c:' + c + ';d:' + d); //c:2;d:1
jsfiddle
var x = 0, y = 0;
//post-increment: i++ returns value then adds one to it
console.log('x++ will log: ', x++); //0
console.log('x after x++ : ', x); //1
//pre-increment: adds one to the value, then returns it
console.log('++y will log: ', ++y); //1
console.log('y after ++y : ', y); //1
It is clearer and faster to use ++i if possible :
++i guarantees that you are using a value of i that will remains the same unless you change i
i++ allows to use a value of i which will change in the "near future", it is not desirable if possible
Of course, it's not really much faster, only a little.
In JavaScript you can use ++ operator before (pre-increment) or after the variable name (post-increment). What, if any, are the differences between these ways of incrementing a variable?
Same as in other languages:
++x (pre-increment) means "increment the variable; the value of the expression is the final value"
x++ (post-increment) means "remember the original value, then increment the variable; the value of the expression is the original value"
Now when used as a standalone statement, they mean the same thing:
x++;
++x;
The difference comes when you use the value of the expression elsewhere. For example:
x = 0;
y = array[x++]; // This will get array[0]
x = 0;
y = array[++x]; // This will get array[1]
++x increments the value, then evaluates and stores it.
x++ evaluates the value, then increments and stores it.
var n = 0, m = 0;
alert(n++); /* Shows 0, then stores n = 1 */
alert(++m); /* Shows 1, then stores m = 1 */
Note that there are slight performance benefits to using ++x where possible, because you read the variable, modify it, then evaluate and store it. Versus the x++ operator where you read the value, evaluate it, modify it, then store it.
As I understand them if you use them standalone they do the same thing. If you try to output the result of them as an expression then they may differ. Try alert(i++) as compared to alert(++i) to see the difference. i++ evaluates to i before the addition and ++i does the addition before evaluating.
See http://jsfiddle.net/xaDC4/ for an example.
I've an explanation of understanding post-increment and pre-increment. So I'm putting it here.
Lets assign 0 to x
let x = 0;
Lets start with post-increment
console.log(x++); // Outputs 0
Why?
Lets break the x++ expression down
x = x;
x = x + 1;
First statement returns the value of x which is 0
And later when you use x variable anywhere, then the second statement is executed
Second statement returns the value of this x + 1 expression which is (0 + 1) = 1
Keep in mind the value of x at this state which is 1
Now lets start with pre-increment
console.log(++x); // Outputs 2
Why?
Lets break the ++x expression down
x = x + 1;
x = x;
First statement returns the value of this x + 1 expression which is (1 + 1) = 2
Second statement returns the value of x which is 2 so x = 2 thus it returns 2
Hope this would help you understand what post-increment and pre-increment are!
var a = 1;
var b = ++a;
alert('a:' + a + ';b:' + b); //a:2;b:2
var c = 1;
var d = c++;
alert('c:' + c + ';d:' + d); //c:2;d:1
jsfiddle
var x = 0, y = 0;
//post-increment: i++ returns value then adds one to it
console.log('x++ will log: ', x++); //0
console.log('x after x++ : ', x); //1
//pre-increment: adds one to the value, then returns it
console.log('++y will log: ', ++y); //1
console.log('y after ++y : ', y); //1
It is clearer and faster to use ++i if possible :
++i guarantees that you are using a value of i that will remains the same unless you change i
i++ allows to use a value of i which will change in the "near future", it is not desirable if possible
Of course, it's not really much faster, only a little.