-
Notifications
You must be signed in to change notification settings - Fork 22.4k
/
index.md
95 lines (73 loc) · 2.56 KB
/
index.md
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
---
title: "SyntaxError: Unexpected token"
slug: Web/JavaScript/Reference/Errors/Unexpected_token
page-type: javascript-error
---
{{jsSidebar("Errors")}}
The JavaScript exceptions "unexpected token" occur when the parser does not see a token it recognizes at the given position, so it cannot make sense of the structure of the program. This might be a simple typo.
## Message
```plain
SyntaxError: Unexpected token ';' (V8-based)
SyntaxError: Unexpected identifier 'x' (V8-based)
SyntaxError: Unexpected number (V8-based)
SyntaxError: Unexpected string (V8-based)
SyntaxError: Unexpected regular expression (V8-based)
SyntaxError: Unexpected template string (V8-based)
SyntaxError: unexpected token: identifier (Firefox)
SyntaxError: expected expression, got "x" (Firefox)
SyntaxError: expected property name, got "x" (Firefox)
SyntaxError: expected target, got "x" (Firefox)
SyntaxError: expected meta, got "x" (Firefox)
SyntaxError: expected rest argument name, got "x" (Firefox)
SyntaxError: expected closing parenthesis, got "x" (Firefox)
```
## Error type
{{jsxref("SyntaxError")}}
## What went wrong?
A specific language construct was expected, but something else was provided. This might
be a simple typo.
## Examples
### Expression expected
For example, when chaining expressions, trailing commas are not allowed.
```js-nolint example-bad
for (let i = 0; i < 5,; ++i) {
console.log(i);
}
// Uncaught SyntaxError: expected expression, got ';'
```
Correct would be omitting the comma or adding another expression:
```js example-good
for (let i = 0; i < 5; ++i) {
console.log(i);
}
```
### Not enough parentheses
Sometimes, you leave out parentheses around `if` statements:
```js-nolint example-bad
function round(n, upperBound, lowerBound) {
if (n > upperBound) || (n < lowerBound) { // Not enough parenthese here!
throw new Error(`Number ${n} is more than ${upperBound} or less than ${lowerBound}`);
} else if (n < (upperBound + lowerBound) / 2) {
return lowerBound;
} else {
return upperBound;
}
} // SyntaxError: expected expression, got '||'
```
The parentheses may look correct at first, but note how the `||` is outside the
parentheses. Correct would be putting parentheses around the `||`:
```js-nolint example-good
function round(n, upperBound, lowerBound) {
if ((n > upperBound) || (n < lowerBound)) {
throw new Error(
`Number ${n} is more than ${upperBound} or less than ${lowerBound}`,
);
} else if (n < (upperBound + lowerBound) / 2) {
return lowerBound;
} else {
return upperBound;
}
}
```
## See also
- {{jsxref("SyntaxError")}}