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rules.jshint.W053.html Maven / Gradle / Ivy

    
When do I get this error?
The "Do not use {a} as a constructor" error is thrown when JSLint, JSHint or
ESLint encounters a call to String, Number, Boolean, Math or JSON
preceded by the new operator. In the following example we attempt to assign
some values to variables by invoking these functions as constructors:
​x
 
1
var str = new String("hello"),
2
    num = new Number(10),
3
    bool = new Boolean(false),
4
    math = new Math(),
5
    json = new JSON({ myProp: 10 });
6
​
JSLint found 5 errors
Which linter should be used for this code snippet:
 JSLint JSHint ESLint
Which version of the linter should be used:
Update
Version 2015-09-23
Line 0:
Unexpected 'new'.
Line 1:
Unexpected 'new'.
Line 2:
Unexpected 'new'.
Line 4:
Unexpected space between '{' and 'myProp'.
Line 4:
Unexpected space between '10' and '}'.

Why do I get this error?
This error is raised to highlight a bad practice and a piece of code that
may not work as you intend it to. It can also highlight a possible fatal
JavaScript error. Your code could run without error if you do not change it,
but could be confusing to other developers and could also behave in unexpected
ways.
The String, Number and Boolean constructor functions return objects of
type String, Number and Boolean, which is rarely what you want. Usually,
you want literal string, number or boolean values, because strictly comparing an
object to a literal will always return false. In the case of these objects, to
fix this error, use literal values rather than their corresponding wrapper
objects:
4
 
1
var str = "hello",
2
    num = 10,
3
    bool = false;
4
​
JSLint found no errors
Which linter should be used for this code snippet:
 JSLint JSHint ESLint
Which version of the linter should be used:
Update
Version 2015-09-23

Note that this does not cause you to lose any functionality, since literal
values are internally cast to instances of the appropriate type when you call a
method on them. Also note that you are free to use these functions to perform
type conversions i.e. by invoking them without the new operator:
4
 
1
var str = String(10),    // "10"
2
    num = Number("123"), // 123
3
    bool = Boolean("");  // false
4
​
JSLint found no errors
Which linter should be used for this code snippet:
 JSLint JSHint ESLint
Which version of the linter should be used:
Update
Version 2015-09-23

The case is a little different for the Math and JSON objects. These two
objects are not functions, and cannot be constructed. Attempts to instantiate
them will result in a type error. If you're trying to serialize an object into a
JSON string, you need to use the JSON.stringify method instead:
2
 
1
var json = JSON.stringify({ myProp: 10 });
2
​
JSLint found 2 errors
Which linter should be used for this code snippet:
 JSLint JSHint ESLint
Which version of the linter should be used:
Update
Version 2015-09-23
Line 0:
Unexpected space between '{' and 'myProp'.
Line 0:
Unexpected space between '10' and '}'.

In JSHint 1.0.0 and above you have the ability to ignore any warning with a
special option syntax. The identifier of this warning is W053.
This means you can tell JSHint to not issue this warning with the /*jshint
-W053 */ directive.