Node: Storing function names in a variable and then calling them - node.js

Question

I am writing a node application that uses node-cron to schedule certain function to run at specific times. Currently the code for this is embedded in the main application. I want to move the configuration of scheduled tasks out to a config file, so want need to store the function names in a variable to achieve this, as the schedule tasks call out a number of functions in different modules etc.
For information the syntax to schedule a cron task is this:
cron.schedule('* * * * *', () => {functiontocall()});
The code block below shows how I am currently storing the tasks in an object and trying to schedule them with node-cron.
mycronobj = [
{scheduletime : "* * * * *", schedulefunction : 'testfunction1'},
{scheduletime : "*/5 * * * *", schedulefunction : 'testfunction2'},
{scheduletime : "*/10 * * * *", schedulefunction : 'testfunction3'},
]
for (item in mycronobj) {
cron.schedule(mycronobj[item].scheduletime, () => {mycronobj[item].schedulefunction()});
}
However this doesn't work, the scheduled functions don't run. I have tried storing the functions names as a string (as shown) or direct as
{scheduletime : "* * * * *", schedulefunction : testfunction1()}
When trying to add the scheduled function I have tried this with the following syntaxes:
mycronobj[item].schedulefunction()
mycronobj[item]schedulefunction
mycronobj[item].schedulefunction
None of which have worked for me. I have tried looking for an answer to this and I tried using eval(), but this also didn't work correctly, the outcome was that a task with first schedule ("* * * * *") was scheduled with the last function 'testfunction3' was applied, also I dont really want to use eval as I have read its not great practice and can be avoided if you know what your doing (clearly I don't).
Other options I have come across is to use Window which doesn't exist in Node or This, which I cannot get to work either.
Thanks in advance.

Answer 1

The reason your code isn't working is that mycronobj[item]schedulefunction is a string so is not invokable. You need to turn this string into a reference to the function with the same name.
The simplest solution to this is using eval, e.g:
for (item of mycronobj) {
cron.schedule(item.scheduletime, () =>
eval(`${item.schedulefunction}()`);
}
However this is a really bad idea, and allows for arbitrary code execution which is generally considered a very bad thing (tm).
Node gives you a slightly safer alternative to this using the vm module, which can create a limited sandbox in which your code can execute:
const vm = require("vm");
let context = vm.createContext({ foo });
for (item of mycronobj) {
cron.schedule(item.scheduletime, () =>
vm.runInContext(`${item.schedulefunction}()`, context);
}
This is only marginally better though since it can still allow arbitrary code execution, so by far the safest option is just to explicitly list exactly which functions are allowed to be called:
const commands = {
testfunction1: () => console.log("I am 1"),
testfunction2: () => console.log("I am 2"),
testfunction3 // Reference existing function
}
function testfunction3() { console.log("I am 3"); }
for (item of mycronobj) {
let func = commands[item.schedulefunction];
if (!func) { throw new Error(`Unknown command: "${item.schedulefunction}"`); }
cron.schedule(item.scheduletime, func);
}
This also has the benefit of determining during setup whether functions are valid rather than only when the cron job runs.