[Feature Request] Flag for disabling implicit coerisions

[redradist]

Search Terms

safe typescript, predictable behavior, no implicit coercion

Suggestion

I would like to suggest to introduce a new flag for disabling implicit type coercion at all
Something like this:

--predicatableJs

Or some other flag

Use Cases

To make Typescript even more safe

I want to enforce my team to use only predictable features and if they want old style behavior, just to write another module or disable warning at the top of the file (in such way all reviewers of this files will see that)

Examples

Instead of writing either:

let strange_boolean: any = true;
let strange_string: string = "1";
console.log(strange_boolean == strange_string);

or

let strange_number: any = 2;
let strange_string: string = "1";
console.log(strange_number == strange_string);

I want to enforce that this code produce error and compiles only if there is explicit cast:

let strange_boolean: any = true;
let strange_string: string = "1";
console.log(String(strange_boolean) == strange_string);

let strange_boolean: any = true;
let strange_string: string = "1";
console.log(Boolean(strange_boolean) == Boolean(strange_string));

let strange_number: any = 2;
let strange_string: string = "1";
console.log(String(strange_number) == strange_string);

let strange_number: any = 2;
let strange_string: string = "1";
console.log(strange_number == Number(strange_string));

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

[RyanCavanaugh]

We're not going to add a flag that causes errors on any, so that's right out. A flag for disabling boolean coercion is discussed at #14114

[redradist]

@RyanCavanaugh

We're not going to add a flag that causes errors on any, so that's right out. A flag for disabling boolean coercion is discussed at #14114

It is not duplicate

I am not taking about boolean coercion, but about coercion at all

I want to enforce users to write by default safe code, that's all

It is possible by enforcing users to use only explicit coercions, but not implicit

let strange_number: any = 2;
let strange_string: string = "1";
console.log(String(strange_number) == strange_string);

or

let strange_number: any = 2;
let strange_string: string = "1";
console.log(Number(strange_number) == Number(strange_string));

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.

[redradist]

@RyanCavanaugh Have you seen my comment ? Will you remove tag Duplicate ?

[redradist]

@ahejlsberg I just want to call to you as Lead of the language ...

Don't you think this Feature Request should be implemented ? This very useful that make TypeScript even more safe ...

[RyanCavanaugh]

@redradist We're tracking this adequately; thank you for the feedback. See also #38905