Methods were accessed during render but is not defined on instance. on vue widget

I have this problem when I can’t work with Vue methods in my Html file it will play the following error to me: “handleEvent” was accessed during render but is not defined on the instance.
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I’m a beginner on Vue widget and I have never faced a problem like this, so I’m stuck
can you help me?

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I think your function might be located in a wrong block like ‘data() { return {here} }’, export default { here } or somewhere