How to transmit an arguments object to a function?

Question

I'm working with handlebars.js and I'd like to format some numbers with a helper. To format a number I've found the accounting.js library that seems to meet my expectations. To format a number I can use:

// Simple `format` string allows control of symbol position (%v = value, %s = symbol):
accounting.formatMoney(5318008, { symbol: "GBP",  format: "%v %s" }); // 5,318,008.00 GBP

Here is my current helper:

Handlebars.registerHelper('amount', function(item) {
    if (item == null) {
        return "-"; 
    } else {    
        return accounting.formatMoney(item,{symbol: "EUR",  format: "%v %s"});                                       
    }
});

This works but this a bit strict in use, I'd like to be able to format my numbers as an option. My new helper would then be :

Handlebars.registerHelper('amount', function(item, options) {
    if (item == null) {
        return "-"; 
    } else {    
        return accounting.formatMoney(item,options);                                       
    }
});

The problem is that it doesn't work because I don't know how to pass the object to the worker. Here is my call in the template

{{amount programme.amountIssued {symbol: "EUR",  format: "%v %s"} }}

This gives me the following result:

handlebars.js:1659 Uncaught Error: Parse error on line 87:
...gramme.amountIssued {symbol: "EUR",  for
-----------------------^
Expecting 'CLOSE_RAW_BLOCK', 'CLOSE', 'CLOSE_UNESCAPED', 'OPEN_SEXPR', 'CLOSE_SEXPR', 'ID', 'OPEN_BLOCK_PARAMS', 'STRING', 'NUMBER', 'BOOLEAN', 'UNDEFINED', 'NULL', 'DATA', 'SEP', got 'INVALID'

If I use it with quotes around and quotes inside commented with \ :

{{amount programme.amountIssued "{symbol: \"EUR\",  format: \"%v %s\"}" }}

This is executed but the result is not the one expected :

{symbol: "EUR", format: "4,000,000,000.00 %s"}%v

instead of 4,000,000,000.00 EUR

General tip: A JS object is **not** the same thing as JSON. Just call it an "object" because that's what is is. It's a common confusion, but these two things are really very different, so it's important not to mix them up. — Tomalak, Apr 26 '16 at 08:32

Tomalak · Accepted Answer · 2016-04-26T08:33:49.843

You can't pass arguments to a JS function with an object. But you can pass them as an array. This is done through .apply (docs).

Wrapped for legibility and including defaults for every option:

Handlebars.registerHelper('amount', function (item, options) {
    if (item == null) return "-"; 

    return accounting.formatMoney.apply(accounting, [
        item,
        options.symbol || "",
        options.precision || 2,
        options.thousands || ".",
        options.decimal || ","
    ]);                                       
});

Here the function is applied to an array of values (hence the name of the operation) where each array position matches the parameter position the function expects.

How to transmit an arguments object to a function?

1 Answers1