fallback.md

ts2wasm-compiler fallback mechanism

The strategy of ts2wasm-compiler is to apply static compilation as much as possible, but there are circumstances where statization is not available, including:

1. The effort to implement static compilation for some object is relatively large, which isn't on high priority (e.g. Map, Set).
2. Accessing efficiency of some object is not critical to the application's overall performance (e.g. Date, JSON).

In this case, ts2wasm-compiler supports a fallback mechanism

• for scenario 1, this serves as a temporary workaround before the statical support is ready.
• for scenario 2, this will be a formal solution to bridge common used JavaScript builtin method to TypeScript application.

Example

export function JSONTest() {
    let json = '{"result":true, "count":42}';
    // The JSON.parse and JSON.stringify are implemented by JS runtime
    let obj = JSON.parse(json);
    let str: string = JSON.stringify(obj) as string;
    console.log(obj.count);
    console.log(str);
}

Fallback whitelist

• JSON object and all methods
• Map constructor and all methods
• Set constructor and all methods
• Date constructor and all methods
• Promise constructor, object and all methods

Note: The list of objects allowed to be fallbacked is restricted by the compiler to reduce test pressure, please contact the developer team if you need more fallback objects