Js object key: plus value syntax

Question

I found this weird syntax in d3 example

var heatmapChart = function(tsvFile) {
    d3.tsv(tsvFile,
    function(d) {
      return {
        day: +d.day,
        hour: +d.hour,
        value: +d.value
      };
    },

What plus in

      day: +d.day,

mean?

How so? Doesn't the duplicate explain what `+` does in front of a value? Or are you asking about something else? — Bergi, Oct 10 '16 at 18:37
You might also want to take a look at [What's the significant use of unary plus and minus operators?](http://stackoverflow.com/q/5450076/1048572) — Bergi, Oct 10 '16 at 18:38

score 0 · Accepted Answer · edited Jun 20 '20 at 09:12

0

This is a unary conversion. It's a shorthand method to convert to a number. From the ECMAScript docs:

The unary + operator converts its operand to Number type.

The production UnaryExpression : + UnaryExpression is evaluated as follows:

Let expr be the result of evaluating UnaryExpression.

Return ToNumber(GetValue(expr)).

var a = "45"; //typeof String
a = +a; // now typeof Number

edited Jun 20 '20 at 09:12

Community

1
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answered Oct 10 '16 at 18:32

Sterling Archer

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Unary plus has nothing to do with concatenation or adding? – Bergi Oct 10 '16 at 18:33
Well damn, you're right. – Sterling Archer Oct 10 '16 at 18:34
1

omg I am really close to giving up with Javascript... Thank you – kurumkan Oct 10 '16 at 18:36

Js object key: plus value syntax

1 Answers1