JS.TS.NO.INFERRABLE.TYPES
Disallows explicit type declarations for variables or parameters initialized to a number, string, or boolean
Explicit types where they can be easily inferred may add unnecessary verbosity.
Rule Details
This rule disallows explicit type declarations on parameters, variables and properties where the type can be easily inferred from its value.
Options
This rule accepts the following options:
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interface Options {
ignoreParameters?: boolean;
ignoreProperties?: boolean;
}
Default
The default options are:
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{
"ignoreParameters": false,
"ignoreProperties": false
}
With these options, the following patterns are:
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Incorrect
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const a: bigint = 10n;
const a: bigint = -10n;
const a: bigint = BigInt(10);
const a: bigint = -BigInt(10);
const a: boolean = false;
const a: boolean = true;
const a: boolean = Boolean(null);
const a: boolean = !0;
const a: number = 10;
const a: number = +10;
const a: number = -10;
const a: number = Number('1');
const a: number = +Number('1');
const a: number = -Number('1');
const a: number = Infinity;
const a: number = +Infinity;
const a: number = -Infinity;
const a: number = NaN;
const a: number = +NaN;
const a: number = -NaN;
const a: null = null;
const a: RegExp = /a/;
const a: RegExp = RegExp('a');
const a: RegExp = new RegExp('a');
const a: string = 'str';
const a: string = `str`;
const a: string = String(1);
const a: symbol = Symbol('a');
const a: undefined = undefined;
const a: undefined = void someValue;
class Foo {
prop: number = 5;
}
function fn(a: number = 5, b: boolean = true) {}
Correct
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const a = 10n;
const a = -10n;
const a = BigInt(10);
const a = -BigInt(10);
const a = false;
const a = true;
const a = Boolean(null);
const a = !0;
const a = 10;
const a = +10;
const a = -10;
const a = Number('1');
const a = +Number('1');
const a = -Number('1');
const a = Infinity;
const a = +Infinity;
const a = -Infinity;
const a = NaN;
const a = +NaN;
const a = -NaN;
const a = null;
const a = /a/;
const a = RegExp('a');
const a = new RegExp('a');
const a = 'str';
const a = `str`;
const a = String(1);
const a = Symbol('a');
const a = undefined;
const a = void someValue;
class Foo {
prop = 5;
}
function fn(a = 5, b = true) {}
function fn(a: number, b: boolean, c: string) {}
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ignoreParameters
When set to true, the following pattern is considered valid:
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function foo(a: number = 5, b: boolean = true) {
// ...
}
ignoreProperties
When set to true, the following pattern is considered valid:
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class Foo {
prop: number = 5;
}
When Not To Use It
If you do not want to enforce inferred types.
Further Reading
TypeScript Inference (https://www.typescriptlang.org/docs/handbook/type-inference.html)
