React native variable declaration

Question

Whats the difference between these way of declaring variables in react-native.

import React, { Component } from 'react';
import { AppRegistry, Image, View, Text, } from 'react-native';
export default class Hello extends Component {
render() {
**const var1 = 'hi';**
return ( );
}}

import React, { Component } from 'react';
import { AppRegistry, Image, View, Text, } from 'react-native';
**const var1 = 'hi';**
export default class Hello extends Component {
render() {
return ( );
}}

Answer 1

The difference between those variables is scope.

In both cases, due to the use of const, var1 will only be accessible after its declaration.

The scope of a const variable is it's running execution context. In your two examples, the execution contexts are different.

In the second example:

import React, { Component } from 'react';
import { AppRegistry, Image, View, Text, } from 'react-native';
const var1 = 'hi';
export default class Hello extends Component {
  render() {
    return ( );
  }
}

The execution context where var1 is declared is the file.

This means that at any point in the file after const var1 = 'hi'; the var1 variable is available and its value is 'hi'.

In your first example:

import React, { Component } from 'react';
import { AppRegistry, Image, View, Text, } from 'react-native';
export default class Hello extends Component {
  render() {
    const var1 = 'hi';
    return ( );
  }
}

The execution context of the declaration is the method render().

Similarly, it means that at any point in the render() method and ONLY inside that render() method after the const var1 = 'hi'; statement the var1 variable is available and its value will be 'hi'.

tl;dr

In summary, when you use const var1 = 'hi'; inside a method, the var1 (constant) variable will only be available inside that method. OTOH, when you declare const var1 = 'hi'; in the file, outside of any class or {} or function, var1 will be available in the whole file.

In both cases, though, var1 will only be defined/available after the const var1 = 'hi'; declaration statement.