Error Prone

AvoidTrailingComma

Since: PMD 5.1

Priority: High (1)

This rule helps improve code portability due to differences in browser treatment of trailing commas in object or array literals.

This rule is defined by the following XPath expression:

//ObjectLiteral[$allowObjectLiteral = "false" and @TrailingComma = 'true']
|
//ArrayLiteral[$allowArrayLiteral = "false" and @TrailingComma = 'true']

Example(s):

function(arg) {
    var obj1 = { a : 1 };   // Ok
    var arr1 = [ 1, 2 ];    // Ok

    var obj2 = { a : 1, };  // Syntax error in some browsers!
    var arr2 = [ 1, 2, ];   // Length 2 or 3 depending on the browser!
}

This rule has the following properties:

Use this rule by referencing it:

<rule ref="category/ecmascript/errorprone.xml/AvoidTrailingComma" />

EqualComparison

Since: PMD 5.0

Priority: Medium (3)

Using == in condition may lead to unexpected results, as the variables are automatically casted to be of the same type. The === operator avoids the casting.

This rule is defined by the following XPath expression:

//InfixExpression[(@Image = "==" or @Image = "!=")
  and
 (child::KeywordLiteral[@Image = "true" or @Image = "false"]
 or
 child::NumberLiteral)
]

Example(s):

// Ok
if (someVar === true) {
  ...
}
// Ok
if (someVar !== 3) {
  ...
}
// Bad
if (someVar == true) {
  ...
}
// Bad
if (someVar != 3) {
  ...
}

Use this rule by referencing it:

<rule ref="category/ecmascript/errorprone.xml/EqualComparison" />

InnaccurateNumericLiteral

Since: PMD 5.0

Priority: Medium High (2)

The numeric literal will have a different value at runtime, which can happen if you provide too much precision in a floating point number. This may result in numeric calculations being in error.

This rule is defined by the following XPath expression:

//NumberLiteral[
    @Image != @Number
    and translate(@Image, "e", "E") != @Number
    and concat(@Image, ".0") != @Number
    and @Image != substring-before(translate(@Number, ".", ""), "E")]

Example(s):

var a = 9; // Ok
var b = 999999999999999; // Ok
var c = 999999999999999999999; // Not good
var w = 1.12e-4; // Ok
var x = 1.12; // Ok
var y = 1.1234567890123; // Ok
var z = 1.12345678901234567; // Not good

Use this rule by referencing it:

<rule ref="category/ecmascript/errorprone.xml/InnaccurateNumericLiteral" />