is it possible to create your own condition/control flow syntax in js? for example:
when( condition ) {
// execute code
}
this would add some sort of listener to a variable/object and execute whenever the condition is true.
I may just have to create my own programming language.
This is actually two questions:
The answer to the first is no. You can use preprocessing like sweet.js macros to accomplish that but its non-trivial.
The answer to 2 is yes, you can accomplish this in any ES 5 compliant environment (IE 9+):
var condition = {val: null};
Object.defineProperty(condition, "isTrue", {
set: function(val) {
if (val && !this.val) {
runSomeCodeYouWantRun();
}
this.val = val;
},
get: function() {
return this.val;
}
});
So whenever any code changes condition.isTrue the specified code will be run if the change is truthy. But for situations like this I prefer less ad-hoc approach. ES 2015 Proxy traps make this much cleaner (IMHO) but support isn't quite there yet. What you really are looking for here to get the job done today is an Observable.
Also note that writing a language to solve a problem like this is roughly equivalent to building a car out of spare parts to drive to the store for groceries. Just buy a car.
JavaScript in and of itself does not have any utilities for creating your own syntax. In response to this, many tools exist online and in the NPM repositories that add just this sort of feature to JS by translating it to browser-compatible JavaScript. Here's a small sampling:
require() functionalityAll of these transpilers, however different, all work the same way: they parse the source file(s) to an abstract syntax tree (or AST), run some transformations on that tree, and then spit out the resulting JavaScript file. If you wanted to create your own special syntax in JavaScript, you would do more or less the same thing. (Uglify.JS stands out as being particularly customizable in this regard).
All of that said, none of these transpilers fundamentally change the way that JavaScript works - you still have to translate whatever fancy syntax you want to use into plain, browser-executable JavaScript. This means that although you will be able to write your when(){} block syntax, the expression inside the parentheses cannot be a simple Boolean expression, but must involve something like an Observable object that inserts a callback (Knockout.JS does have a tool for doing this out of an expression built from its Observables).
