no-obj-calls

Disallow calling global object properties as functions

ECMAScript provides several global objects that are intended to be used as-is. Some of these objects look as if they could be constructors due their capitalization (such as Math and JSON) but will throw an error if you try to execute them as functions.

The ECMAScript 5 specification makes it clear that both Math and JSON cannot be invoked:

The Math object does not have a [[Call]] internal property; it is not possible to invoke the Math object as a function.

The ECMAScript 2015 specification makes it clear that Reflect cannot be invoked:

The Reflect object also does not have a [[Call]] internal method; it is not possible to invoke the Reflect object as a function.

The ECMAScript 2017 specification makes it clear that Atomics cannot be invoked:

The Atomics object does not have a [[Call]] internal method; it is not possible to invoke the Atomics object as a function.

And the ECMAScript Internationalization API Specification makes it clear that Intl cannot be invoked:

The Intl object does not have a [[Call]] internal method; it is not possible to invoke the Intl object as a function.

Rule Details

This rule disallows calling the Math, JSON, Reflect, Atomics and Intl objects as functions.

This rule also disallows using these objects as constructors with the new operator.

Examples of incorrect code for this rule:

/*eslint no-obj-calls: "error"*/
/*eslint-env es2017, browser */

var math = Math();

var newMath = new Math();

var json = JSON();

var newJSON = new JSON();

var reflect = Reflect();

var newReflect = new Reflect();

var atomics = Atomics();

var newAtomics = new Atomics();

var intl = Intl();

var newIntl = new Intl();
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Examples of correct code for this rule:

/*eslint no-obj-calls: "error"*/
/*eslint-env es2017, browser*/

function area(r) {
    return Math.PI * r * r;
}

var object = JSON.parse("{}");

var value = Reflect.get({ x: 1, y: 2 }, "x");

var first = Atomics.load(foo, 0);

var segmenterFr = new Intl.Segmenter("fr", { granularity: "word" });
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Handled by TypeScript

It is safe to disable this rule when using TypeScript because TypeScript's compiler enforces this check.

Version

This rule was introduced in ESLint v0.0.9.

Further Reading

Annotated ES5
es5.github.io

Resources

• Rule source
• Tests source