escpos-templates v0.2.0

escpos-templates

🖨️ Template engine for easily formatting node-escpos receipts

Installation

Add the escpos-templates package to your project:

yarn add escpos-templates
# or
npm install escpos-templates

Usage

Instantiate EscPosTemplate with the template text, then provide it with a printer instance and your variables to directly drive the printer interface:

import {EscPosTemplate} from "node-escpos-templates";
import {Printer, Network} from "escpos";

const device = new Network("127.0.0.1", 1234);
const printer = new Printer(device);

const template = new EscPosTemplate(`print \"Hello {{theName}}!"; feed 2; cut;`);
const myVars = {theName: "Bob"};

device.open((err) => {
  // Directly drive printer instructions from the template, with optional variables
  template.print(printer, myVars);
  printer.close();
});

Creating templates

This project uses a simple custom syntax to define print templates.

Each print instruction must be placed on separate line, and/or seperated with a semicolon ;.

"Hello world" example

A very simple template that prints some text, beeps once, then cuts the paper:

Template text:

print "Hello world!";
beep 1 1;
cut;

Working with variables

When calling print() you can provide an object of template variables.

You can refer to these anywhere in a template string by using the {{variableName}} syntax. You can also refer to variables directly as arguments to template functions.

Template text:

# Print "Bob" 
print name;

# Print "Hello Bob!"
print "Hello {{name}}!";

# Print "Hello Bob Smith!"
print "Hello {{person.firstName}} {{person.lastName}}!";

Code:

template.print(printer, {name: "Bob", person: {firstName: "Bob", lastName: "Smith"}});

Most functions expect integers or string values, but some special functions like images and tables may need special input (refer to the function list below for details).

Printing special elements

Images

To print an image, you'll need to prepare an escpos.Image instance in advance and pass it as a variable:

Code and template text:

import {Image} from "escpos";

Image.load("hippopotamus.png", function (hippoImg) {
  const template = new EscPosTemplate("init; align center; image hippoImg; feed 5; cut");

  device.open((err) => {
    template.print(printer, { hippoImg });
    printer.close();
  });
});

Barcodes

Supported barcodes (depending on printer model) are UPC_A, UPC_E, EAN13, EAN8, CODE39, ITF, NW7, CODE93, and CODE128.

Template text:

# Print EAN-13 barcode
barcode "EAN13" "ABCDEF123456" 2 50

The arguments for the barcode function are: type, code, width (optional, range 2 - 6), height (optional, range 1-255), text position (optional, defaults to "below") and barcode font ("A" or "B").

Text position options are: off (no text), above (text above barcode), below (text below barcode), both (text above and below barcode).

Iterating through data

When you pass an array as a variable, you can iterate through it using a loop statement. This can be useful for line items.

Template text:

loop myArray
  # In the iteration context, each array item is available as "item"
  # You can access keys on variables as well for more flexibility
  print item.label
endloop 

Code:

template.print(printer, {myArray: [{label: "One"}, {label: "Two"}, {label: "Three"}]});
// Prints "One", "Two" and "Three" each on a seperate line

Begin iterating over an array variable with the loop statement. Each following statement, until endloop the statement, will be executed for each item in the array, with item as variable for each array element.

If-statements

The template syntax has limited support for if-statements. They allow you to make a set of instructions conditional on whether a variable is truthy or not.

Template text:

if varOne

  # If varOne is truthy, this instruction will execute...
  print "One!"
  
  # You can also nest statements!
  if varTwo
    print "Also, two?"
  endif
  
endif

Code:

template.print(printer, {varOne: "This is truthy", varTwo: 0});
// Prints "One!"

Function list

These are the functions that are currently implemented for use in the templates.

Arguments are listed in [brackets], with optional arguments denoted with a ?.

Core

Text formatting

Special elements

Additional information

Template syntax

Some details about the template syntax this library uses:

• Each line is evaluated separately;
  • Empty lines are ignored
  • Lines that start with a hash # are ignored (comment)
• Each line is parsed for instructions;
  • Multiple instructions can be split using a semicolon ;
  • Each instruction starts with an alphanumeric opcode (e.g. print)
  • Each instruction can have any amount of arguments, split by a space or tab
• Each argument can be passed as a string literal or variable;
  • Double quotes should " wrap around a string literal
  • Backslash \ can be used as an escape character anywhere
  • Any argument that isn't a string literal must be an integer or variable reference
  • Some variables are predefined (e.g. true, false and options listed in the table above)
  • If hexadecimal notation (0x) is used in place of a variable, it is automatically resolved to the corresponding character
• When using a loop, all instructions are buffered and will not be evaluated until the endloop statement is evaluated;
• When using an if, the argument is evaluated to check whether it is Truthy or not; if it's not, all statements following it until the endif will be skipped (but must still have valid syntax);
  • Nested if-statements are supported

Special settings

Parity bit (barcodes)

You can globally control whether a parity bit is included for certain barcode types. It is enabled by default but may not be supported by some printers:

EscPosTemplate.setEnableBarcodeParityBit(false); // turn parity bit OFF for all barcodes