Disallow negated left operand of 'in' operator

Disallow Global Object Function Calls

Disallow usage of NaN directly

Ensure type checks are against valid types

Assignment to function name not allowed

Do not do toString directly on method objects

Disallow use of delete on variables

Catch identifiers should be unique

Ambiguous named function expression

Export not at module level

Numeric literal causes overflow or underflow exception

Strict operator always evaluates to true or false

Array literal trailing commas has cross-browser difference

Variable or function declaration redefines the catch error name

Constant declaration already declared

Duplicate lexical declaration; cannot redefine let or const variables

High-surrogate pair value not followed by low-surrogate value

Reserved words and should not be used as an identifier

Low-surrogate pair value not preceeded by high-surrogate value

Function declaration should not be inside a statement. Cross-browser behavior difference

Reserved word used as object literal property name; cross-browser issue

Identifier already in use

Octal literals are deprecated. Possible cross-browser behavior difference

New line not allowed

Imported module does not export name

Semicolon insertion

A statement block is expected

Suspect assigment

Strict-mode does not allow certain variable names

Strict-mode does not allow certain function names

Strict-mode does not allow duplicate property names

Strict-mode does not allow assignment to certain variables

Strict-mode does not allow ++ or -- on certain objects

Strict-mode does not allow certain delete operands

Strict-mode does not allow certain argument names

Assignment to constant

String literal is not safe for inline

Strict-mode does not allow assignment to undefined variables

End of file encountered before function is properly closed

Expected ///#ENDIF directive

Expected ///#ENDDEBUG directive

Invalid numeric literal

Suspect equality comparison

Strict-mode does not allow certain catch error binding names

Binding patterns in var statements require initializer

Implicit object property name must be identifier

Setter method must have a single format argument

Rest parameter can only be last parameter

Unable to convert to binding syntax

Unable to convert from binding syntax

Invalid binding syntax

Methods not allowed in object literal bindings

Expected for or if keyword

Expected class element

Duplicate class element name

Class constructor must be regular method

Class static method cannot be named 'prototype'

Expected binding

Multiple default exports

Import statement must include module name

Duplicate module declaration

Imported module has no default export

Expected 'from'

Expected string literal

Expected specifier set

Arrow functions cannot be constructors

Application Error

No Source Error

Could not parse JavaScript code

Syntax error

Expected ':'

Expected ';' between statements

Syntax error in regular expression

Invalid character

Unterminated string constant

Unterminated comment

'return' statement outside of function

Can't have 'break' outside of loop

Can't have 'continue' outside of loop

unused label

Expected hexadecimal digit

Expected 'while'

Label redefined

Label not found

'default' can only appear once in a 'switch' statement

Expected identifier or string

Expected '@end'

Conditional compilation is turned off

Expected 'catch'

Unmatched 'else'; no 'if' defined

Expected ','

Missing 'case' or 'default' statement

Unmatched '@end'; no '@if' defined

Unmatched '@else'; no '@if' defined

Unmatched '@elif'; no '@if' defined

Expecting more source characters

Too many tokens have been skipped in the process of recovering from errors. The file may not be a JScript.NET file

Did you intend to have an empty statement for this branch of the if statement?

A variable argument list must be the last argument

Function expression expected

JSParser Exception

Resource reference must be single constant value

Conditiona compilation structure too complex

Unterminated ASP.NET block

Strict-mode does not allow with-statements

Strict-mode does not allow duplicate argument names

Disallow negated left operand of 'in' operator

This is an error, if one intended this usage it should be explicitly coerced

CheckId	SPC018906
TypeName	DisallowNegatedLeftOperandOfInOperator
Severity	Warning
Type	JavaScriptFile

Resolution

Bad Practice

if(!a in b) {
return false;
}

Good Practice

if(!(a in b)) {
return false;
}
// or if you intended to !aif(('' + !a) in b) {
return false;
}