JSHint 配置参数浅析

This option prohibits the use of bitwise operators such as ^ (XOR), | (OR) and others. Bitwise operators are very rare in JavaScript programs and quite often & is simply a mistyped &&.

This option allows you to force all variable names to use either camelCase style or UPPER_CASE with underscores.

This option requires you to always put curly braces around blocks in loops and conditionals. JavaScript allows you to omit curly braces when the block consists of only one statement, for example:

while (day)
  shuffle();

However, in some circumstances, it can lead to bugs (you'd think that sleep() is a part of the loop while in reality it is not):

while (day)
  shuffle();
  sleep();

This option is a short hand for the most strict JSHint configuration as available in JSHint version 2.6.3. It enables all enforcing options and disables all relaxing options that were defined in that release.

This options prohibits the use of == and != in favor of === and !==. The former try to coerce values before comparing them which can lead to some unexpected results. The latter don't do any coercion so they are generally safer. If you would like to learn more about type coercion in JavaScript, we recommend Truth, Equality and JavaScript by Angus Croll.

This option tells JSHint that your code needs to adhere to ECMAScript 3 specification. Use this option if you need your program to be executable in older browsers—such as Internet Explorer 6/7/8/9—and other legacy JavaScript environments.

This option enables syntax first defined in the ECMAScript 5.1 specification. This includes allowing reserved keywords as object properties.

This option requires all for in loops to filter object's items. The for in statement allows for looping through the names of all of the properties of an object including those inherited through the prototype chain. This behavior can lead to unexpected items in your object so it is generally safer to always filter inherited properties out as shown in the example:

for (key in obj) {
  if (obj.hasOwnProperty(key)) {
    // We are sure that obj[key] belongs to the object and was not inherited.
  }
}

For more in-depth understanding of for in loops in JavaScript, read Exploring JavaScript for-in loops by Angus Croll.

This options prohibits overwriting prototypes of native objects such as Array, Date and so on.

// jshint freeze:true
Array.prototype.count = function (value) { return 4; };
// -> Warning: Extending prototype of native object: 'Array'.

This option suppresses warnings about declaring variables inside of control structures while accessing them later from the outside. Even though JavaScript has only two real scopes—global and function—such practice leads to confusion among people new to the language and hard-to-debug bugs. This is why, by default, JSHint warns about variables that are used outside of their intended scope.

function test() {
  if (true) {
    var x = 0;
  }

  x += 1; // Default: 'x' used out of scope.
            // No warning when funcscope:true
}

This option enables warnings about the use of identifiers which are defined in future versions of JavaScript. Although overwriting them has no effect in contexts where they are not implemented, this practice can cause issues when migrating codebases to newer versions of the language.

This option can be used to specify a white list of global variables that are not formally defined in the source code. This is most useful when combined with the undef option in order to suppress warnings for project-specific global variables.

Setting an entry to true enables reading and writing to that variable. Setting it to false will trigger JSHint to consider that variable read-only.

See also the "environment" options: a set of options to be used as short hand for enabling global variables defined in common JavaScript environments.

This option prohibits the use of immediate function invocations without wrapping them in parentheses. Wrapping parentheses assists readers of your code in understanding that the expression is the result of a function, and not the function itself.

This option sets a specific tab width for your code.

This option suppresses warnings about the __iterator__ property. This property is not supported by all browsers so use it carefully.

This option prohibits the use of a variable before it was defined. JavaScript has function scope only and, in addition to that, all variables are always moved—or hoisted— to the top of the function. This behavior can lead to some very nasty bugs and that's why it is safer to always use variable only after they have been explicitly defined.

Setting this option to "nofunc" will allow function declarations to be ignored.

For more in-depth understanding of scoping and hoisting in JavaScript, read JavaScript Scoping and Hoisting by Ben Cherry.

This option lets you control cyclomatic complexity throughout your code. Cyclomatic complexity measures the number of linearly independent paths through a program's source code. Read more about cyclomatic complexity on Wikipedia.

This option lets you control how nested do you want your blocks to be:

// jshint maxdepth:2

function main(meaning) {
  var day = true;

  if (meaning === 42) {
    while (day) {
      shuffle();

      if (tired) { // JSHint: Blocks are nested too deeply (3).
          sleep();
      }
    }
  }
}

This options allows you to set the maximum amount of warnings JSHint will produce before giving up. Default is 50.

This option lets you set the maximum length of a line.

This option lets you set the max number of formal parameters allowed per function:

// jshint maxparams:3

function login(request, onSuccess) {
  // ...
}

// JSHint: Too many parameters per function (4).
function logout(request, isManual, whereAmI, onSuccess) {
  // ...
}

This option lets you set the max number of statements allowed per function:

// jshint maxstatements:4

function main() {
  var i = 0;
  var j = 0;

  // Function declarations count as one statement. Their bodies
  // don't get taken into account for the outer function.
  function inner() {
    var i2 = 1;
    var j2 = 1;

    return i2 + j2;
  }

  j = i + j;
  return j; // JSHint: Too many statements per function. (5)
}

This option requires you to capitalize names of constructor functions. Capitalizing functions that are intended to be used with new operator is just a convention that helps programmers to visually distinguish constructor functions from other types of functions to help spot mistakes when using this.

Not doing so won't break your code in any browsers or environments but it will be a bit harder to figure out—by reading the code—if the function was supposed to be used with or without new. And this is important because when the function that was intended to be used with new is used without it, this will point to the global object instead of a new object.

This option prohibits the use of arguments.caller and arguments.callee. Both .caller and .callee make quite a few optimizations impossible so they were deprecated in future versions of JavaScript. In fact, ECMAScript 5 forbids the use of arguments.callee in strict mode.

This option prohibits the use of the comma operator. When misused, the comma operator can obscure the value of a statement and promote incorrect code.

This option warns when you have an empty block in your code. JSLint was originally warning for all empty blocks and we simply made it optional. There were no studies reporting that empty blocks in JavaScript break your code in any way.

This option warns about "non-breaking whitespace" characters. These characters can be entered with option-space on Mac computers and have a potential of breaking non-UTF8 web pages.

This option prohibits the use of constructor functions for side-effects. Some people like to call constructor functions without assigning its result to any variable:

new MyConstructor();

There is no advantage in this approach over simply calling MyConstructor since the object that the operator new creates isn't used anywhere so you should generally avoid constructors like this one.

This option suppresses warnings about invalid typeof operator values. This operator has only a limited set of possible return values. By default, JSHint warns when you compare its result with an invalid value which often can be a typo.

// 'fuction' instead of 'function'
if (typeof a == "fuction") { // Invalid typeof value 'fuction'
  // ...
}

Do not use this option unless you're absolutely sure you don't want these checks.

This option enforces the consistency of quotation marks used throughout your code. It accepts three values: true if you don't want to enforce one particular style but want some consistency, "single" if you want to allow only single quotes and "double" if you want to allow only double quotes.

This option suppresses warnings about variable shadowing i.e. declaring a variable that had been already declared somewhere in the outer scope.

• "inner" - check for variables defined in the same scope only

• "outer" - check for variables defined in outer scopes as well

• false - same as inner

• true - allow variable shadowing

This option prohibits the use of the grouping operator when it is not strictly required. Such usage commonly reflects a misunderstanding of unary operators, for example:

// jshint singleGroups: true

delete(obj.attr); // Warning: Unnecessary grouping operator.

This option requires all functions to run in ECMAScript 5's strict mode. Strict mode is a way to opt in to a restricted variant of JavaScript. Strict mode eliminates some JavaScript pitfalls that didn't cause errors by changing them to produce errors. It also fixes mistakes that made it difficult for the JavaScript engines to perform certain optimizations.

Note: This option enables strict mode for function scope only. It prohibits the global scoped strict mode because it might break third-party widgets on your page. If you really want to use global strict mode, see the globalstrict option.

This option prohibits the use of explicitly undeclared variables. This option is very useful for spotting leaking and mistyped variables.

// jshint undef:true

function test() {
  var myVar = 'Hello, World';
  console.log(myvar); // Oops, typoed here. JSHint with undef will complain
}

If your variable is defined in another file, you can use the global directive to tell JSHint about it.

This option warns when you define and never use your variables. It is very useful for general code cleanup, especially when used in addition to undef.

// jshint unused:true

function test(a, b) {
  var c, d = 2;

  return a + d;
}

test(1, 2);

// Line 3: 'b' was defined but never used.
// Line 4: 'c' was defined but never used.

In addition to that, this option will warn you about unused global variables declared via the global directive.

This can be set to vars to only check for variables, not function parameters, or strict to check all variables and parameters. The default (true) behavior is to allow unused parameters that are followed by a used parameter.

When set to true, the use of VariableStatements are forbidden. For example:

// jshint varstmt: true

var a; // Warning: `var` declarations are forbidden. Use `let` or `const` instead.