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Vue.js is a very popular JavaScript framework designed to help developers build efficient and flexible web applications. Vue.js provides two different modes: strict mode and non-strict mode. These two modes are very different in the development and deployment of Vue.js. Let's take a closer look.

1. What is the strict mode of Vue.js?

Vue.js's strict mode is a development mode that forces developers to follow some strict rules to ensure the correctness and maintainability of the code. In strict mode, Vue.js will warn or report some common errors and non-standard code. These errors include:

1. Modify the state of the component directly in the rendering function.

2. Modify other properties directly in the computed property.

3. Modify other properties directly in the created hook function.

4. Using undefined variables or functions.

5. Use index as key in v-for loop.

In strict mode, Vue.js will warn or report the above errors to help developers find and solve problems faster and improve the readability and maintainability of the code.

2. What is Vue.js's non-strict mode?

Vue.js's non-strict mode is a development mode that allows developers to write code in some non-standard ways, such as directly modifying the state of a component or modifying other properties in a computed property. In non-strict mode, Vue.js will not warn or report errors for these non-standard codes, which allows developers to write code more flexibly, but also brings certain risks and unpredictability.

3. Give examples to illustrate the difference between strict mode and non-strict mode of Vue.js

Below we use a simple example to illustrate the difference between strict mode and non-strict mode of Vue.js.

Suppose we have a component whose template looks like this:

<template>
  <div>
    <p>{{ message }}</p>
    <button @click="changeMessage">Change Message</button>
  </div>
</template>

In this component, we have a data property message, whose initial value is "Hello, Vue.js". We also define a method changeMessage, which can modify the value of message. In non-strict mode, we can implement it like this:

<script>
export default {
  data() {
    return {
      message: 'Hello, Vue.js'
    };
  },
  methods: {
    changeMessage() {
      this.message = 'Hello, World';
    }
  }
}
</script>

In non-strict mode, the above code can run normally, but in strict mode, Vue.js will report a warning, reminding us that we should not modify the state of the component directly in the method. Therefore, in strict mode, we need to use the $set method provided by Vue.js to modify the state of the component. The code is as follows:

<script>
export default {
  data() {
    return {
      message: 'Hello, Vue.js'
    };
  },
  methods: {
    changeMessage() {
      this.$set(this, 'message', 'Hello, World');
    }
  }
}
</script>

From the above examples, we can see that in strict mode, Vue.js will warn or report errors for some non-standard codes to ensure the correctness and maintainability of the code. In non-strict mode, Vue.js allows developers to have some non-standard writing methods, but it also brings certain risks and unpredictability, so developers need to weigh the pros and cons.