How do you represent a number as a string in javascript?

Question

I have a node-red flow that needs to create an MQTT payload.

The payload is a temperature reading from an I/O card, calculated as a float (73.4 for example).

I need the message payload to be a string, not a number; something like "Barn Temp is 73.2". How can I create this?

msg.payload = tempReading;               // gives a number
msg.payload = ""+tempReading;            // returns NaN

A bonus question: if I did use this as a numeric payload how can I specify its format? The reading is calculated at 73.18527461364; I need to send this as 73.2.

I'm having a devil of a time finding out how to format strings in javascript!

String + Number produces string. Example doesn't make sense unless `tempReading` is `NaN` in second one — charlietfl, Jan 30 '17 at 20:58
Possible duplicate of [JavaScript string and number conversion](http://stackoverflow.com/questions/971039/javascript-string-and-number-conversion) — Sandesh, Jan 30 '17 at 20:58
And `.toFixed()` lets you truncate the fractional part (returning a string) — Pointy, Jan 30 '17 at 20:59
Thanks for the shortcuts. I see where the person who posed the referenced answer was bashed for asking a question as well. — buzzard51, Jan 30 '17 at 21:37

score 1 · Accepted Answer · answered Jan 30 '17 at 20:59

1

toString is an easy surefire way to convert numbers to strings.

var x = 10.56;
x = x.toString();
console.log(x, typeof x);

If you want to control how many decimal points are displayed, you can use toFixed.

var x = 12.3456789;
x = x.toFixed(3);
console.log(x, typeof x);

answered Jan 30 '17 at 20:59

Mike Cluck

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I'd love to improve my answer if someone could explain what's wrong with it. – Mike Cluck Jan 30 '17 at 21:09
Perfect! And msg.payload=reading.toFixed(1).toString() worked as well. – buzzard51 Jan 30 '17 at 21:32

score 0 · Answer 2 · answered Jan 30 '17 at 23:56

0

var num = 74.3; //=> typeof num "number"

var converted = String(num); //=> typeof converted "string" "74.3"

In your case, just do:

msg.payload = String(tempReading);

answered Jan 30 '17 at 23:56

johnny_mac

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How do you represent a number as a string in javascript?

2 Answers2