Can I catch (trigger event) when a certain function in a big, uneditable library is called?
// big js library
var biglibrary = {
runme: function(arguments){
// do something...
},
otherfunctions: function(.....
}
Now how can I outside above catch / notice when runme is called? Can I? I tried something like this ->
$(biglibrary).on('runme', function(){
// function was called !!!
});
In the vast majority of cases, you can wrap the function:
const original = biglibrary.runme;
biglibrary.runme = function(...args) {
console.log("Function was called!");
return original.apply(this, args);
};
const biglibrary = {
runme: function(a, b) {
console.log(`Original function: ${a} + ${b}`);
return a + b;
},
};
const original = biglibrary.runme;
biglibrary.runme = function(...args) {
console.log("Function was called!");
return original.apply(this, args);
}
console.log(biglibrary.runme(1, 2));This is sometimes called "monkey-patching."
In some cases, the library may have made the runme property read-only, in which case you might be able to wrap it via Object.defineProperty:
const original = biglibrary.runme;
const descr = Object.getOwnPropertyDescriptor(biglibrary, "runme");
descr.value = function(...args) {
console.log("Function was called!");
return original.apply(this, args);
}
Object.defineProperty(biglibrary, "runme", descr);
const biglibrary = {
runme: function(a, b) {
console.log(`Original function: ${a} + ${b}`);
return a + b;
},
};
const original = biglibrary.runme;
const descr = Object.getOwnPropertyDescriptor(biglibrary, "runme");
descr.value = function(...args) {
console.log("Function was called!");
return original.apply(this, args);
}
Object.defineProperty(biglibrary, "runme", descr);
console.log(biglibrary.runme(1, 2));If the library has made the property both read-only and non-configurable, you can't wrap it, but that's rare.