[Vuejs]-Unexpected side effect vue

It’s coming from “eslint-plugin-vue” and the link for that rule is below,

https://eslint.vuejs.org/rules/no-side-effects-in-computed-properties.html

Either you override this rule in your eslint rules file or you can simply turn off the eslint for this specific line like below

this.days = Object.keys(this.response.prices)[index]; // eslint-disable-line

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One more thing (Not related to your question) is that you need to return some value in computed.