JavaScript 中「匯出預設值」的威力是什麼以及如何有效使用它？

Unlocking the Power of "export default" in JavaScript

Within the vast landscape of JavaScript, there lies a powerful concept known as "export default." It allows developers to effortlessly share a single value as the default export of a module, simplifying the module import process.

Consider the example below:

// File: SafeString.js
function SafeString(string) {
  this.string = string;
}

SafeString.prototype.toString = function() {
  return "" + this.string;
};

export default SafeString;

Equivalent Exports Made Simple

If the syntax of "export default" seems unfamiliar, there are other, equivalent ways to achieve the same result. Let's explore two alternatives:

1. Named Exports: This technique involves assigning a specific name to the exported value, as seen in the modified code below:

// File: SafeString.js
export const SafeString = function(string) {
  this.string = string;
};

SafeString.prototype.toString = function() {
  return "" + this.string;
};

2. Object Export (Prior to ES6): In versions of JavaScript preceding ES6, you could export a default value by assigning it to a property on an exported object:

// File: SafeString.js
module.exports = {
  default: function(string) {
    this.string = string;
  }
}

Usage with Imports

Regardless of the export method used, importing the default value is consistent. Simply omit the curly braces when importing the module:

import SafeString from "SafeString";

This import statement will assign the default value exported from the "SafeString" module to the "SafeString" variable in the current module.

Conclusion

"export default" is a powerful tool in JavaScript, allowing developers to share values as the default export of a module. Understanding its syntax and its equivalent export methods is crucial for unlocking its full potential in modular development.

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