Build javascript chain as text but execute as script

Question

I'm working with this print library. What I'm trying to do now is build up my print payload. Right now when it's no dynamic it looks like this:

serialPort.on('open',function() {
var printer = new Printer(serialPort);
printer.on('ready', function() {
    printer
        .printLine('text line 1')
        .printLine('text line 2')
        .printLine('text line 3')
        .print(function() {
            console.log('done');
            //do other stuff
        });
});
});

The issue I'm having is figuring out how to build up my print payload so that I can dynamcially create my string of .whatever().whatever().print() to actually do the printing.

I ran across this post and came up with the following code but get the error Uncaught ReferenceError: printLine is not defined which makes sense but I don't really know where to go from here.

So.....Basically what I'm asking is, what's a good way to build up a chained function call without it actually being executed as javascript until I trigger it?

var buildLine = Function("input", "printLine('input')");
var lineItems = ['hello', 'world'];
var printPayload = '';
_.map(lineItems, function(item) {
  printPayload += buildLine(item)

})
console.log(printPayload);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.10.1/lodash.min.js"></script>

[There is always eval()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval), but I can't say I recommend it. — faino, Jan 03 '16 at 21:00
There are multiple ways of doing `.whatever().whatever().print()`; some are much larger security holes than others, if you're including user-provided values, or values from outside libraries (or even including things, just on the page, like banner ads); do you have an *exact*, *concrete example* of **what you want to provide, how you want to chain it, and what you want it to print, based on the input and instructions**? — Norguard, Jan 03 '16 at 21:02

adeneo · Accepted Answer · 2016-01-03T21:03:10.333

This is confusing, and seems a bit like an X/Y problem.

I think you want to just store the object in a variable, and then chain on another function at a later time

serialPort.on('open', function() {

    var printer = new Printer(serialPort),
        intance;

    printer.on('ready', function() {
        intance = printer.printLine('text line 1')
                         .printLine('text line 2')
                         .printLine('text line 3');
    });

    something.on('later_event', function() {
        instance.print(function() {
            // done
        });
    });
});

And looking at the plugin, it has a commandQueue where it stores all added commands, so you don't really have to store anything, each instance keeps track of the added commands automatically

serialPort.on('open', function() {

    var printer   = new Printer(serialPort);
    var lineItems = ['hello', 'world'];

    printer.on('ready', function() {

        lineItems.forEach(function(line) {

             printer.printLine(line);

        });

    });

    something.on('later_event', function() {
        printer.print(function() {
            // done
        });
    });
});

Right, that makes more senses, but how do I build up the "string" of function calls that comprise `intance` ? Because intance needs to be created dynamically. — Justin Young, Jan 03 '16 at 21:03

Build javascript chain as text but execute as script

1 Answers1