Error: Unable to access length property of null object. Can you explain this to me?

One of my questions that I'm trying to solve is about the error message "Cannot read properties of null (reading 'transition'). What does it mean?". I tried using the solution suggested in this question on integration of 'mychart.update()': https://github.com/chartjs/Chart.js/issues/5149. However, I encountered another error when I tried to implement it.

TypeError: Cannot read properties of null (reading 'length')
    at Object.acquireContext (Chart.js?473e:7756:1)
    at Chart.construct (Chart.js?473e:9324:1)
    at new Chart (Chart.js?473e:9311:1)
    at VueComponent.draw (Analytics-test.vue?b2a7:69:1)
    at VueComponent.loadTrainings (Analytics-test.vue?b2a7:444:1)
    at async VueComponent.mounted (Analytics-test.vue?b2a7:476:1)

Below is the last code I attempted to run:

<template>
  <div> Profit/Attendance <div class="small">
      <canvas id="mychart" height="400"></canvas>
    </div>
  </div>
</template>
...

And also, I tried this alternative option:

<template>
  <div> Profit/Attendance <div class="small">
      <canvas id="mychart" height="400"></canvas>
    </div>
  </div>
</template>
...

When I examined the string in the debugger, I found references to specific lines of code. The last reference pointed to this line:

https://i.sstatic.net/ZRHYJ.png

Further investigation led me to this line of code:

https://i.sstatic.net/3lrwd.png

Answer №1

In relation to Arrays, the length property is utilized. However, the issue arises when attempting to read a value that is null. This occurs when the const or var containing that property becomes null due to various reasons.

Answer №2

The issue was related to the template. I forgot to input the correct id for the canvas element. It should be like this:

<canvas id="main-chart" height="400"></canvas>

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