如何使用数组变量更新对象值？ （JavaScript）

Question

I have an object variable storing bar chart values and a button to update those values:

  var config = { type: 'bar', data: { datasets: [{ type: 'bar', label: 'Dataset 1', data: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]}]}}; document.getElementById('add5').addEventListener('click', function() { tnow = moment().format('HH'); switch (tnow) { case'8': config.data.datasets[0].data[0] += 5; break; case'9': config.data.datasets[0].data[1] += 5; break; // ... case'23': config.data.datasets[0].data[15] += 5; break; case'24': config.data.datasets[0].data[16] += 5; break; default: alert('doot');} window.myLine.update()}); 

  <button id="add5">+5</button> 

I seek to store the value pointer as a variable to shorten the code. Tried

var h = [];
var h = config.data.datasets[0].data.slice();

but

case '23': h[15] += 5; break;

does not update the bar chart value. alert(h[15]) does, however, return the accurate chart value.

How can I update the chart values using array variables?

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FULL CONTEXT:

Using moment.js and chart.js to generate a bar graph that updates a value according to a real-time clock. Ex: if it's 7:30PM, clicking '+5' will add 5 to the bar located at 7PM. case '8' = 8AM, case '23' = 11PM, etc. I intend to add a second dataset which gets displayed when values exceed 60, using an if to modify the second dataset's value ( involving config.data … twice more - making the code pretty lengthy).

Answer 1

When you use slice() :

var h = config.data.datasets[0].data.slice();

you are making a copy of config.data.datasets[0].data . You then alter that copy in your code, but this has no effect on the bar chart because it doesn't change the original data:

 let datasets = [{ data: [1, 2, 3, 4, 5, 6] }] let h = datasets[0].data.slice() h[0] ="What?" console.log(h) // h has changed console.log(datasets[0].data) // original data is unchanged console.log(h === datasets[0].data) // because they are not the same array 

If you want to shorten your code, just take a reference to the array without slice() :

var h = config.data.datasets[0].data

 let datasets = [{ data: [1, 2, 3, 4, 5, 6] }] let h = datasets[0].data h[0] ="What?" console.log(h) // h has changed console.log(datasets[0].data) // original data is also chaged console.log(h === datasets[0].data) // because they ARE the same array