Employing various Class Methods based on the chosen target compiler option

Question

Employing various Class Methods based on the chosen target compiler option

Is there a way to instruct TypeScript to utilize different implementations of methods within the same class, based on the specified target option in the tsconfig.json file?

I am currently transitioning one of my scripts to TypeScript to streamline management of codebases by consolidating an ES5 and an ES6 file into a single source. Due to TypeScript's ability to switch output targets in the tsconfig.json file, I aim to have a single version that can be easily updated and maintained.

The challenge arises from using a generator in the ES6 version, which should not pose a problem as TypeScript automatically adds a pseudo-generator to the top of the ES5 output. However, my current Pseudo-Generator implementation in the ES5 file is more concise and clean.

Possible Solutions

Is there a method to override the respective "generator" method or use specialized comment annotations (such as //@ts-target) to specify which code (function body) to use based on the selected target in the configuration file, even if it is not documented officially?

Integrating an additional function or script into the TypeScript compiler process may provide assistance since I compile both ES files through a small node.js script without directly altering the tsconfig.json file.

Alternatively, is there an extension available to segregate different methods of a class into separate files? This would enable extraction of the respective "generator" methods. However, this approach raises questions regarding linking them based on the target, given that I utilize /// <reference /> linking in the main script file for consolidation.

Any innovative suggestions?

class Option {
    ///@ts-target ES5
    __walkerVariable1:any undefined
    __walkerVariable2:any undefined
    __walkerVariable3:any undefined
    walker() {
        /* Pseudo-Walker Code for ES5 */
    }

    ///@ts-target ES6
    *walker() {
        /* Real Walker Code for ES6 */
    }
}

Currently, a Pseudo-Generator code is injected into the ES5 version of my script. I aspire to address this challenge by implementing a different method/function that houses my personal Pseudo-Generator. Therefore, I seek guidance on how to instruct TypeScript to disregard the Pseudo-Generator in ES6/Real-Generator in ES5 and only include one of them based on the chosen target option.

javascript typescript class

Answer 1

Answer №1

After some careful consideration, I managed to tackle a tricky problem by seeking guidance from an informative GitHub issue.

In my approach, I utilize a custom node.js script to compile TypeScript files into two distinct JavaScript versions, ES5 and ES6. This involves leveraging the TypeScript API and utilizing the ts.createProgram method, which allows for the integration of a host object as a third parameter. The host object facilitates various compiler processes, including the file loader method known as getSourceFile.

The remainder of the process is relatively straightforward: I employ regular expressions to identify and filter custom comment annotations such as \\\@ts-target:ES5 and \\\@ts-target:ES6. While it may not be the most elegant solution, it effectively achieves the desired outcome!

function compileTS(){
    let config = readConfig("ts/tsconfig.json");
    let host = ts.createCompilerHost(config.options);
    let sourceFile = host.getSourceFile;

    // Generating ES5 JavaScript
    (function(config){
        host.getSourceFile = function(filename) {
            if(filename === "ts/options.ts"){
                let file = fs.readFileSync("./ts/options.ts").toString();
                file = file.replace(/[ ]+\/\/\/\@ts\-target\:ES6\s+([\s\S]*)\/\/\/\@ts\-target\:ES6/gm, "");
                return ts.createSourceFile(filename, file, ts.ScriptTarget.ES5, true);
            }
            return sourceFile.call(host, filename);
        }
        let program = ts.createProgram(config.fileNames, config.options, host);
        let emitResult = program.emit();
        report(ts.getPreEmitDiagnostics(program).concat(emitResult.diagnostics));
        if(emitResult.emitSkipped){
            process.exit(1);
        }
    }(config));

    // Generating ES6 JavaScript
    config.options.target = 2;
    config.options.outFile = "../dist/js/tail.select-es6.js";
    (function(config){
        host.getSourceFile = function(filename) {
            if(filename === "ts/options.ts"){
                let file = fs.readFileSync("./ts/options.ts").toString();
                file = file.replace(/[ ]+\/\/\/\@ts\-target\:ES5\s+([\s\S]*)\/\/\/\@ts\-target\:ES5/gm, "");
                return ts.createSourceFile(filename, file, ts.ScriptTarget.ES2015, true);
            }
            return sourceFile.call(host, filename);
        }
        let program = ts.createProgram(config.fileNames, config.options, host);
        let emitResult = program.emit();
        report(ts.getPreEmitDiagnostics(program).concat(emitResult.diagnostics));
        if(emitResult.emitSkipped){
            process.exit(1);
        }
    }(config));
}

Answer 2

After some careful consideration, I managed to tackle a tricky problem by seeking guidance from an informative GitHub issue.

In my approach, I utilize a custom node.js script to compile TypeScript files into two distinct JavaScript versions, ES5 and ES6. This involves leveraging the TypeScript API and utilizing the ts.createProgram method, which allows for the integration of a host object as a third parameter. The host object facilitates various compiler processes, including the file loader method known as getSourceFile.

The remainder of the process is relatively straightforward: I employ regular expressions to identify and filter custom comment annotations such as \\\@ts-target:ES5 and \\\@ts-target:ES6. While it may not be the most elegant solution, it effectively achieves the desired outcome!

function compileTS(){
    let config = readConfig("ts/tsconfig.json");
    let host = ts.createCompilerHost(config.options);
    let sourceFile = host.getSourceFile;

    // Generating ES5 JavaScript
    (function(config){
        host.getSourceFile = function(filename) {
            if(filename === "ts/options.ts"){
                let file = fs.readFileSync("./ts/options.ts").toString();
                file = file.replace(/[ ]+\/\/\/\@ts\-target\:ES6\s+([\s\S]*)\/\/\/\@ts\-target\:ES6/gm, "");
                return ts.createSourceFile(filename, file, ts.ScriptTarget.ES5, true);
            }
            return sourceFile.call(host, filename);
        }
        let program = ts.createProgram(config.fileNames, config.options, host);
        let emitResult = program.emit();
        report(ts.getPreEmitDiagnostics(program).concat(emitResult.diagnostics));
        if(emitResult.emitSkipped){
            process.exit(1);
        }
    }(config));

    // Generating ES6 JavaScript
    config.options.target = 2;
    config.options.outFile = "../dist/js/tail.select-es6.js";
    (function(config){
        host.getSourceFile = function(filename) {
            if(filename === "ts/options.ts"){
                let file = fs.readFileSync("./ts/options.ts").toString();
                file = file.replace(/[ ]+\/\/\/\@ts\-target\:ES5\s+([\s\S]*)\/\/\/\@ts\-target\:ES5/gm, "");
                return ts.createSourceFile(filename, file, ts.ScriptTarget.ES2015, true);
            }
            return sourceFile.call(host, filename);
        }
        let program = ts.createProgram(config.fileNames, config.options, host);
        let emitResult = program.emit();
        report(ts.getPreEmitDiagnostics(program).concat(emitResult.diagnostics));
        if(emitResult.emitSkipped){
            process.exit(1);
        }
    }(config));
}

Employing various Class Methods based on the chosen target compiler option

Answer №1

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