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Jose Hermosilla Rodrigo
Asked: 2020-08-04 07:02:27 +0800 CST 2020-08-04 07:02:27 +0800 CST

TypeScript - Function calls without parentheses?

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I am relatively new to TypeScript and am reviewing both documentación oficialthe GitHub.

In one of these GitHub examples there is a function urithat passes arguments without using parentheses ( ejemplo completo):

public async getRateLimit() {
    return this.get<RateLimit>(uri`/rate_limit`);
}

Here is the implementation of this function:

function uri(template: TemplateStringsArray, ...args: any[]): string;
function uri(template: TemplateStringsArray) {
    let text = template[0];
    for (let i = 1; i < template.length; i++) {
        text += encodeURIComponent(String(arguments[i]));
        text += template[i];
    }
    return text;
}

I can't see this way of calling functions documented anywhere. I would really appreciate a link to the documentation or an explanation if I'm wrong.

funciones

1 Answers

  1. Best Answer

    This is not a Typescript feature as such but an ECMAScript 6 feature called tagged template literals .

    A more advanced form of string templates are those that contain a post-processing function. With them it is possible to modify the output of the templates, using a function. The first argument contains an array with the template strings. The second and subsequent arguments are the processed (already cooked) values ​​of the template expressions. Finally, the function returns the manipulated text string. The function name is nothing special, any function name can be used instead.

    var a = 1;
var b = 2;

function procesador(cadenas, ...valores) {
  console.log('Texto:', cadenas);
  console.log('Valores interpolados:', valores);

  return "La salida es " + valores.join(',');
}

console.log(procesador `Texto ${ a + b } entrada ${ a * b}`);

    Typescript developers usually try to support native language features as much as possible since Typescript always compiles to javascript so it would not be a good idea to remove features from the base language. This is a quote from an old news story but it gives you an idea of ​​the goals of the language developers and in which version that change occurred.

    In addition to improving the type system, one of the main goals for the TypeScript 2.0 release is to fully support the ECMAScript 6 standard. With TypeScript 1.4, we take further steps in this direction. In this version we have added a new exit mode for ES6, support for letand constand support for ES6 template strings.

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