JavaScript syntax errors compared (2021)

; instead of ,

Object literal properties are separated by commas (,). Semicolons (;) are not allowed. The following code uses a semicolon instead of a colon in an object literal:

$('.view-content').hoverscroll({
    arrows: true,
    arrowsOpacity: 0.7;
});

Tip: Hover over the message on the right to show the error on the left.

5/5: Ba, qljs, and TS did a great job. They suggested a solution to the problem.

3/5: ESL and V8 reported the problem but did not suggest a solution.

1/5: JSC and SM suggested incorrect solutions.

Invalid object literal key

Object literal property names must be simple identifiers or quoted strings. The following code example tries to create a nested object by writing a dot (.) in the property name:

var company = new Company({
  name: body.name,
  address: body.address,
  friends.name: body.friendName,
  statuses: { status: "New" },
});

Tip: Hover over the tool names below to focus on the errors above.

None of the tools suggested the correct solution to the problem.

4/5: SM reported the problem and suggested a possible solution. However, the suggestion would lead to more syntax errors.

3/5: JSC reported the problem and suggested a possible solution. However, the message is ambiguous because it reports only a line number and because the line contains two '.' characters.

3/5: ESL and V8 reported the problem but did not suggest a solution.

1/5: Ba, qljs, and TS and suggested incorrect solutions. qljs also crashed.

Newline after return

If return is immediately followed by a newline character, undefined is returned, and the following code is interpreted as more statements. The following code expects the return statement to return an object literal:

var homeModelTemplate = function(){
    return
    {
        fromDateSearch: new Date(),
        toDateSearch: new Date()
    };
};

5/5: qljs did a great job. It reported the real problem and hinted at the solution. qljs also reported unrelated errors.

2/5: ESL, JSC, SM, and V8 reported a symptom of the problem, but did not guide the programmer toward a fix.

1/5: Ba and TS suggested incorrect solutions.

Missing ( ) around parameter

If an arrow function has a single parameter, and that parameter is an object destructuring, parentheses are required around the parameter. The following code omits the parentheses:

colls.map({id, ...other} => {
  return preview({
    key: id,
    ...other
  });
})

5/5: SM did a great job. It suggested a solution to the problem.

4/5: JSC and V8 hinted at a solution to the problem, but the message isn't as clear as SM's.

3/5: ESL reported the problem but did not suggest a solution.

1/5: Ba and TS suggested incorrect solutions. TS also reported unrelated errors.

1/5: qljs reported no error at all.

Keyword variable name

With a few exceptions for legacy reasons, function parameters cannot be named a keyword. The following code tries to name a function parameter class, which is a keyword:

function Classes(class, sched) {
  this.class = class;
  this.scheduled = sched;
}

5/5: JSC and TS clearly reported the problem and hinted at a solution. TS also reported unrelated errors.

3/5: Ba, ESL, qljs, and V8 reported the problem but did not suggest a solution. qljs also crashed.

1/5: SM suggested an incorrect solution.

Missing || between expressions

Expressions can't be next to each other without an operator in between. The following code is missing the logical or operator (||) between two expressions in the while loop:

while( s2[Y]=="#" || s2[Y+1] =="X" s3[Y]=="#" || s3[Y+1] =="X");

None of the tools suggested the correct solution to the problem.

3/5: ESL and V8 reported the problem but did not suggest a solution.

1/5: Ba, JSC, qljs, SM, and TS suggested incorrect solutions to the problem.

elseif instead of else if

elseif is a keyword in some languages, but not in JavaScript. The correct code is else if (two words). The following code uses elseif by mistake:

var car;
if(input.val() == "Lamborghini") {
    car = 389;
}elseif(input.val() == "Ferrari"){
    car = 349;
}else{
    car = 0;
}

3/5: qljs reported that the if keyword was missing or misplaced. However, qljs also suggested an incorrect solution to the problem.

2/5: ESL, JSC, SM, and V8 reported an unrelated problem but did not suggest a solution.

1/5: Ba and TS suggested incorrect solutions to the problem.

Missing , between object properties

Object literals have a comma (,)-separated key-value pairs. The following code forgets a comma between two properties:

$.ajax({
  url: "loadcontent1.php",
  data: {
    lastid: 'postitem',
  }
  success: function(html) {
    $("#content").append(html);
  }
});

5/5: qljs did a great job. It suggested a solution to the problem.

4/5: Ba and TS also suggested a solution to the problem, but at a worse location than qljs.

3/5: ESL and V8 reported the problem but did not suggest a solution.

1/5: JSC and SM suggested incorrect solutions.