how to capture the output that a function prints to the terminal in typescript/node

Question

I am working with a typescript/node.js codebase, where there is a function that is called normally:

func('param1', 'param2', param3')

This function does not have a return value but it will print different kinds of output to the terminal when the code is run - this output might be normal console.log statements or an error of some sort. I want to be able to capture whatever the function print out into a variable for use later on - does anyone know how to capture what the function outputs into a variable? (so I can use it in if statments later)

Answer 1

If the function use console.log to output the values, you can override it as:

console.lg = console.log;

console.log = function(arg)
{
    console.lg(arg);
    global.myOutput = arg;
};

Then call your function and after that, check the value of global.myOutput. Also, you can pass all this logic into an object:

const logCapture = {
 output: null,
 enable() {
  console.lg = console.log;
  const that = this;

  console.log = function(arg) {
    console.lg(arg);
    that.output = arg;
   };
 },
 getOutput() {
  return this.output;
 },
 disable() {
  console.log = console.lg;
  console.lg = undefined;
 }
}

And use it:

logCapture.enable();
callToFunction(...);
let myVar = logCapture.getOutput();
logCapture.disable();