10 Essential Vue.js Interview Questions *

Toptal sourced essential questions that the best Vue.js developers and engineers can answer. Driven from our community, we encourage experts to submit questions and offer feedback.

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Interview Questions

Explain the difference between slots and scoped slots.

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A slot is a placeholder in a child component that is filled with content passed from the parent. Content of a regular slot is compiled in the parent’s scope and then passed to the child component.

Thus you can’t use child component properties in a slot’s content. But scoped slots allow you to pass child component data to the parent scope and then use that data in slot content.

Explain Vue.js reactivity and common issues when tracking changes.

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All properties defined in a Vue instance’s data option are reactive, meaning that if they change, the component is automatically updated and re-rendered as needed.

All such properties are converted to getters and setters during initialization, thus allowing Vue to detect when those properties are accessed or changed.

The following limitations must be accounted for when designing a Vue app:

Vue cannot detect object property addition or deletion due to a JavaScript limitation, so the Vue.set method must be used to add new root-level reactive properties.
Similarly, Vue cannot detect when an array item is modified using an index. Vue.set must be used here as well.

What are mixins? Describe their benefits and drawbacks.

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Mixin support is a feature that allows code reuse between components in a Vue.js application and a software composition tool.

A mixin is a JavaScript object that can contain any option that a component can contain. All mixin content is merged with a component’s options when that component uses a mixin.

Mixins help with following the DRY (don’t repeat yourself) principle. A mixin can even be applied globally to every component instance. In that case, it’s called a global mixin.

Mixins are a powerful tool, but some caution is needed while using them. As with all injected code, we should be careful to avoid maintenance issues and unexpected behavior.

It helps to implement mixins using pure functions that don’t modify anything outside their own scope.

Global mixins should be avoided, as affecting every single component can lead to maintenance issues as an application grows. Injecting specific mixins to components as needed leads to more maintainable code.

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What is a single-file component?

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A single-file component is a file with a .vue extension that contains a Vue component. It contains the component’s template, logic, and styles all bundled together in one file. It consists of one