How to use json_encode to format PHP to javascript for Chart?

Question

I would like to convert a PHP array with json_encode to use values in javascript Chart.js

What I have is:

$dataSets = [ 0 => [
    'type' => 'line',
    'data' => json_encode(array_values($val_ca_1), JSON_NUMERIC_CHECK),
    'backgroundColor' => 'transparent',
    'borderColor' => '#007bff',
    'pointBorderColor' => '#007bff',
    'pointBackgroundColor' => '#007bff',
    'fill' => false
  ],

];

With $val_ca_1 = array('2021-02-01' => 10, '2021-02-02' => 14, '2021-02-03' => 8);

What I do in javascript:

new Chart($visitorsChart, {
data: {
  labels: ['2021-02-01', '2021-02-02', '2021-02-03'],
  datasets: <?php echo json_encode($dataSets); ?>
},
options: {
  maintainAspectRatio: false,
  tooltips: {
    mode: mode,
    intersect: intersect
  },

But it displays:

data: {
  labels: ['2021-02-01', '2021-02-02', '2021-02-03'],
  datasets: [{
     "type": "line",
     "data": "[10,14,8]"
     "backgroundColor": "transparent",
     "borderColor": "#007bff",
     "pointBorderColor": "#007bff",
     "pointBackgroundColor": "#007bff",
     "fill": false
  }]
},

And there is a problem with 'data', it has to be:

"data": [10,14,8]

(without double quotes) Any idea? Thanks!

If you remove the json_encode() in 'data' => json_encode does that help, you should be encoding the whole array structure and not just one parts at a time. — Nigel Ren
– Nigel Ren, Commented Feb 15, 2021 at 15:57

ADyson · Accepted Answer · 2021-02-15 16:00:30Z

3

You're double-encoding some of the data. Look at this:

json_encode(array_values($val_ca_1), JSON_NUMERIC_CHECK)

That will pre-encode that part of the data as a string inside $dataSets. So it's already JSON. When you come to convert the whole of $dataSets to JSON, it treats it as the simple string it's already been converted to, rather than an array.

The solution is simple - don't encode different parts of the data separartely. Keep it all in PHP variables and then turn all of it into a JSON string right at the last moment, when you actually need to.

In practical terms, in your code, just change

'data' => json_encode(array_values($val_ca_1), JSON_NUMERIC_CHECK)

to

'data' => array_values($val_ca_1)

answered Feb 15, 2021 at 16:00

ADyson

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