Node.js Object on the server is not an object on the client

Question

I have a variable on the server side of Node.js that is an object. I can verify this with console.log(typeof(value)); and i get object.

When I do a console.log(value); I get

[ 'bla_bla_1',
  'bla_bla_2',
  'bla_bla_3',
]

Then I pass the variable to the client with Express: res.render('target.ejs', {data:value}); and the ejs file parses it with var value = '<%= data %>';

I want to know if it is an object or an array, in order to figure out how to handle it on the client side.

I wrote a little script to test it:

if (typeof(value) === 'object') {console.log("IT'S AN OBJECT");}
else {console.log("IT'S NOT AN OBJECT");}
if ( Array.isArray(value) ) {console.log("IT'S AN ARRAY");}
else {console.log("IT'S NOT AN ARRAY");}

What I get back is this in the console of the browser:

IT'S NOT AN OBJECT
IT'S NOT AN ARRAY

Possible duplicate of [Pass variables to JavaScript in ExpressJS](https://stackoverflow.com/questions/16098397/pass-variables-to-javascript-in-expressjs) — zmag, Aug 19 '19 at 00:21

zmag · Accepted Answer · 2019-08-19T00:16:36.667

2

The value is a simple string after getting parsed with EJS syntax.

EJS Doc specifies how to set a value as it is.

<%- Outputs the unescaped value into the template

Try below:

var value = <%- JSON.stringify(data) %>;

edited Aug 19 '19 at 00:16

answered Aug 18 '19 at 19:44

zmag

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I get this error in the console: "Uncaught SyntaxError: Unexpected token & in JSON at position 1 at JSON.parse ()" – user1584421 Aug 18 '19 at 21:12
@user1584421 You also need to `JSON.stringify` the value on the server prior to sending it to the client. – Kyle Aug 18 '19 at 22:25
Thanks! But now i got both "IT'S AN OBJECT" and "IT'S AN ARRAY". – user1584421 Aug 19 '19 at 16:40
@user1584421 Yes it is. *JavaScript Array* is an object and an array at the same time :) – zmag Aug 19 '19 at 19:35
Thanks! Does this mean i can iterate just like it would be a normal array? And can i run array methods like array.length? – user1584421 Aug 19 '19 at 20:49
@user1584421 Sure. It is an array so you can use methods of Array. – zmag Aug 19 '19 at 22:49

score 2 · Answer 2 · answered Aug 18 '19 at 21:53

From MDN:

Property names must be double-quoted strings; trailing commas are forbidden.

That means you need to replace invalid chars before parsing:

var origvalue = "[ 'bla_bla_1','bla_bla_2','bla_bla_3', ]";
var value =  JSON.parse(origvalue.replace(/'/g, '"').replace(/,[^,]*\]/, '\]'));
if (typeof(value) === 'object') {console.log("IT'S AN OBJECT");}
else {console.log("IT'S NOT AN OBJECT");}
if ( Array.isArray(value) ) {console.log("IT'S AN ARRAY");}
else {console.log("IT'S NOT AN ARRAY");}

score 2 · Answer 3 · answered Aug 18 '19 at 22:44

Objects have “{“ and “}” const obj = { Key2: “value” }

And arrays have [ ]

Objects have key value, arrays don’t, but if you are an orthodox person then you’ll know that at the of the day and array is an object

Do not trust me on this but I think typeof is used on primitive values, and as we know arrays an objects are not, there for is better to use instanceof

Node.js Object on the server is not an object on the client

3 Answers3