| Does const declare a variable? |
const foo = 1;
typeof foo === 'number';
|
Yes |
Yes |
Yes |
Yes |
No |
Yes |
Yes |
| Does const declare a variable? (strict mode) |
'use strict';
const foo = 1;
typeof foo === 'number';
|
SyntaxError: Use of const in strict mode. |
No |
No |
SyntaxError: Unexpected keyword 'const'. Const declarations are not supported in strict mode. |
No |
Yes |
Yes |
|
| Does const make var immutable? |
const foo = 1;
foo = 2;
foo === 1;
|
Yes |
Yes |
Yes |
No |
n/a |
Yes |
Yes |
| Does const make var immutable? (strict mode) |
'use strict';
const foo = 1;
foo = 2;
|
n/a |
n/a |
n/a |
n/a |
n/a |
Yes |
Yes |
|
| Does let declare a variable? |
let foo = 1;
typeof foo === 'number';
|
SyntaxError: Unexpected identifier |
SyntaxError: Illegal let declaration outside extended mode |
SyntaxError: missing ; before statement |
SyntaxError: Unexpected identifier 'foo' |
No |
Unexpected identifier |
Illegal let declaration outside extended mode |
| Does let declare a variable? (strict mode) |
'use strict';
let foo = 1;
typeof foo === 'number';
|
SyntaxError: Unexpected strict mode reserved word |
No |
SyntaxError: let is a reserved identifier |
SyntaxError: Unexpected use of reserved word 'let' in strict mode |
No |
SyntaxError: Unexpected strict mode reserved word |
Yes |
|
| Is let block-local? |
if (1) { let foo = 1; }
typeof foo === 'undefined';
|
n/a |
n/a |
n/a |
n/a |
Yes |
n/a |
n/a |
| Is let block-local? (strict mode) |
'use strict';
if (1) { let foo = 1; }
typeof foo === 'undefined';
|
n/a |
Yes |
n/a |
n/a |
Yes |
n/a |
Yes |
|
| Does let declare non-writable variable? |
if (x) {
let foo = 1;
let foo = '1';
typeof foo === 'number';
}
|
n/a |
n/a |
n/a |
n/a |
No |
n/a |
n/a |
| Does let create non-writeable variable? (strict mode) |
'use strict';
if (x) {
let foo = 1;
let foo = '1';
typeof foo === 'number';
}
|
n/a |
n/a |
n/a |
n/a |
No |
n/a |
Yes |
|
Is let block-local in type="application/javascript;version=1.8"? |
{ let foo = 1; }
typeof foo === 'undefined';
|
Doesn't run |
Doesn't run |
Yes |
Doesn't run |
Doesn't run |
n/a |
n/a |
Is let block-local in type="application/javascript;version=1.8" (strict mode)? |
'use strict';
{ let foo = 1; }
typeof foo === 'undefined';
|
Doesn't run |
Doesn't run |
Yes |
Doesn't run |
Doesn't run |
n/a |
n/a |