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Why does 0.-5 evaluate to -5?

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9

2

Suppose I write 0.5 as 0.-5 in unexpected way, but it can still run. What does 0. in 0.-5 do so that it can still run and evaluates to -5?

I also tried alert(0.-5+1) which prints -4, does JavaScript ignore 0. in 0.-5?

javascript numbers

share|improve this question

edited 34 mins ago

Community♦

11

asked 6 hours ago

mmmaaammmaaa

2,2461312

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  0. is like 0.0. Or just 0.
  
  – Ry-♦
  6 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  What makes you think that 0.-5 is an "unexpected way"?
  
  – Nico Haase
  54 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @NicoHaase: I'm pretty sure the OP used "unexpected way" to mean "I did not intend/expect to write that, but somehow I did".
  
  – Filip Milovanović
  28 mins ago
  

  
  
  
  

add a comment | 

9

2

Suppose I write 0.5 as 0.-5 in unexpected way, but it can still run. What does 0. in 0.-5 do so that it can still run and evaluates to -5?

I also tried alert(0.-5+1) which prints -4, does JavaScript ignore 0. in 0.-5?

javascript numbers

share|improve this question

edited 34 mins ago

Community♦

11

asked 6 hours ago

mmmaaammmaaa

2,2461312

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  0. is like 0.0. Or just 0.
  
  – Ry-♦
  6 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  What makes you think that 0.-5 is an "unexpected way"?
  
  – Nico Haase
  54 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @NicoHaase: I'm pretty sure the OP used "unexpected way" to mean "I did not intend/expect to write that, but somehow I did".
  
  – Filip Milovanović
  28 mins ago
  

  
  
  
  

add a comment | 

Suppose I write 0.5 as 0.-5 in unexpected way, but it can still run. What does 0. in 0.-5 do so that it can still run and evaluates to -5?

I also tried alert(0.-5+1) which prints -4, does JavaScript ignore 0. in 0.-5?

javascript numbers

share|improve this question

edited 34 mins ago

Community♦

11

asked 6 hours ago

mmmaaammmaaa

2,2461312

share|improve this question

edited 34 mins ago

Community♦

11

asked 6 hours ago

mmmaaammmaaa

2,2461312

share|improve this question

edited 34 mins ago

Community♦

11

asked 6 hours ago

mmmaaammmaaa

2,2461312

edited 34 mins ago

Community♦

11

edited 34 mins ago

Community♦

11

asked 6 hours ago

mmmaaammmaaa

2,2461312

asked 6 hours ago

mmmaaammmaaa

2,2461312

4 Answers
4

active

oldest

votes

20

Trailing digits after a . are optional:

console.log(0. === 0);

So

0.-5

evalutes to

0 - 5

which is just -5. Similarly,

0.-5+1

is

0 - 5 + 1

which is

-5 + 1

or -4.

share|improve this answer

answered 6 hours ago

CertainPerformanceCertainPerformance

88.9k154877

add a comment | 

2

In JS you can express a number with optional decimal point.

x = 5.;    //5

x = 5. + 6.   //11

And as of Tvde1's comment, any Number methods can be applied too.

5..toString()

share|improve this answer

edited 1 hour ago

answered 5 hours ago

Charlie HCharlie H

9,05342550

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  You can even do 5..toString().
  
  – Tvde1
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  If fact, you have to do 5..toString() to call the method, otherwise, you have to use parenthesis: (5).toString()
  
  – jo_va
  33 mins ago
  

  
  
  
  

add a comment | 

0

0.-5 could be successfully parsed as 0., - and 5. Below is the abstract syntax tree for the expression:

This (in an unexpected way) is valid JavaScript and evaluates to -5.

share

edited 4 mins ago

answered 9 mins ago

Salman ASalman A

182k66339433

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  And what is wrong with that?
  
  – Salman A
  3 mins ago
  

  
  
  
  

add a comment | 

-1

The trailing dot can be used to call a method directly on a number. Normally you would wrap it in parentheses to isolate the dot, because JavaScript syntax implies the decimal part after the first dot. If you place more two dots, then JavaScript knows the decimal part is empty and the second dot is here to call a method. See this for more information.

console.log((5).toString());

console.log(5..toString());

If you omit the dot, you will get an error:

console.log(5.toString())

share|improve this answer

answered 18 mins ago

jo_vajo_va

4,6531726

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  "The trailing dot can be used to call a method directly on a number" — The trailing dot here is a decimal point.
  
  – Quentin
  5 mins ago
  

  
  
  
  

add a comment | 

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20

Trailing digits after a . are optional:

console.log(0. === 0);

So

0.-5

evalutes to

0 - 5

which is just -5. Similarly,

0.-5+1

is

0 - 5 + 1

which is

-5 + 1

or -4.

share|improve this answer

answered 6 hours ago

CertainPerformanceCertainPerformance

88.9k154877

add a comment | 

20

Trailing digits after a . are optional:

console.log(0. === 0);

So

0.-5

evalutes to

0 - 5

which is just -5. Similarly,

0.-5+1

is

0 - 5 + 1

which is

-5 + 1

or -4.

share|improve this answer

answered 6 hours ago

CertainPerformanceCertainPerformance

88.9k154877

add a comment | 

Trailing digits after a . are optional:

console.log(0. === 0);

So

0.-5

evalutes to

0 - 5

which is just -5. Similarly,

0.-5+1

is

0 - 5 + 1

which is

-5 + 1

or -4.

share|improve this answer

answered 6 hours ago

CertainPerformanceCertainPerformance

88.9k154877

console.log(0. === 0);

0.-5

0 - 5

0.-5+1

0 - 5 + 1

-5 + 1

console.log(0. === 0);

console.log(0. === 0);

share|improve this answer

answered 6 hours ago

CertainPerformanceCertainPerformance

88.9k154877

answered 6 hours ago

CertainPerformanceCertainPerformance

88.9k154877

answered 6 hours ago

CertainPerformanceCertainPerformance

88.9k154877

2

In JS you can express a number with optional decimal point.

x = 5.;    //5

x = 5. + 6.   //11

And as of Tvde1's comment, any Number methods can be applied too.

5..toString()

share|improve this answer

edited 1 hour ago

answered 5 hours ago

Charlie HCharlie H

9,05342550

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  You can even do 5..toString().
  
  – Tvde1
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  If fact, you have to do 5..toString() to call the method, otherwise, you have to use parenthesis: (5).toString()
  
  – jo_va
  33 mins ago
  

  
  
  
  

add a comment | 

2

In JS you can express a number with optional decimal point.

x = 5.;    //5

x = 5. + 6.   //11

And as of Tvde1's comment, any Number methods can be applied too.

5..toString()

share|improve this answer

edited 1 hour ago

answered 5 hours ago

Charlie HCharlie H

9,05342550

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  You can even do 5..toString().
  
  – Tvde1
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  If fact, you have to do 5..toString() to call the method, otherwise, you have to use parenthesis: (5).toString()
  
  – jo_va
  33 mins ago
  

  
  
  
  

add a comment | 

In JS you can express a number with optional decimal point.

x = 5.;    //5

x = 5. + 6.   //11

And as of Tvde1's comment, any Number methods can be applied too.

5..toString()

share|improve this answer

edited 1 hour ago

answered 5 hours ago

Charlie HCharlie H

9,05342550

x = 5.;    //5

x = 5. + 6.   //11

5..toString()

share|improve this answer

edited 1 hour ago

answered 5 hours ago

Charlie HCharlie H

9,05342550

answered 5 hours ago

Charlie HCharlie H

9,05342550

answered 5 hours ago

Charlie HCharlie H

9,05342550

0

0.-5 could be successfully parsed as 0., - and 5. Below is the abstract syntax tree for the expression:

This (in an unexpected way) is valid JavaScript and evaluates to -5.

share

edited 4 mins ago

answered 9 mins ago

Salman ASalman A

182k66339433

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  And what is wrong with that?
  
  – Salman A
  3 mins ago
  

  
  
  
  

add a comment | 

0

0.-5 could be successfully parsed as 0., - and 5. Below is the abstract syntax tree for the expression:

This (in an unexpected way) is valid JavaScript and evaluates to -5.

share

edited 4 mins ago

answered 9 mins ago

Salman ASalman A

182k66339433

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  And what is wrong with that?
  
  – Salman A
  3 mins ago
  

  
  
  
  

add a comment | 

0.-5 could be successfully parsed as 0., - and 5. Below is the abstract syntax tree for the expression:

This (in an unexpected way) is valid JavaScript and evaluates to -5.

share

edited 4 mins ago

answered 9 mins ago

Salman ASalman A

182k66339433

share

edited 4 mins ago

answered 9 mins ago

Salman ASalman A

182k66339433

answered 9 mins ago

Salman ASalman A

182k66339433

answered 9 mins ago

Salman ASalman A

182k66339433

-1

The trailing dot can be used to call a method directly on a number. Normally you would wrap it in parentheses to isolate the dot, because JavaScript syntax implies the decimal part after the first dot. If you place more two dots, then JavaScript knows the decimal part is empty and the second dot is here to call a method. See this for more information.

console.log((5).toString());

console.log(5..toString());

If you omit the dot, you will get an error:

console.log(5.toString())

share|improve this answer

answered 18 mins ago

jo_vajo_va

4,6531726

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  "The trailing dot can be used to call a method directly on a number" — The trailing dot here is a decimal point.
  
  – Quentin
  5 mins ago
  

  
  
  
  

add a comment | 

-1

The trailing dot can be used to call a method directly on a number. Normally you would wrap it in parentheses to isolate the dot, because JavaScript syntax implies the decimal part after the first dot. If you place more two dots, then JavaScript knows the decimal part is empty and the second dot is here to call a method. See this for more information.

console.log((5).toString());

console.log(5..toString());

If you omit the dot, you will get an error:

console.log(5.toString())

share|improve this answer

answered 18 mins ago

jo_vajo_va

4,6531726

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  "The trailing dot can be used to call a method directly on a number" — The trailing dot here is a decimal point.
  
  – Quentin
  5 mins ago
  

  
  
  
  

add a comment | 

The trailing dot can be used to call a method directly on a number. Normally you would wrap it in parentheses to isolate the dot, because JavaScript syntax implies the decimal part after the first dot. If you place more two dots, then JavaScript knows the decimal part is empty and the second dot is here to call a method. See this for more information.

console.log((5).toString());

console.log(5..toString());

If you omit the dot, you will get an error:

console.log(5.toString())

share|improve this answer

answered 18 mins ago

jo_vajo_va

4,6531726

console.log((5).toString());

console.log(5..toString());

console.log(5.toString())

console.log((5).toString());

console.log(5..toString());

console.log((5).toString());

console.log(5..toString());

console.log(5.toString())

console.log(5.toString())

share|improve this answer

answered 18 mins ago

jo_vajo_va

4,6531726

answered 18 mins ago

jo_vajo_va

4,6531726

answered 18 mins ago

jo_vajo_va

4,6531726