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Value Is Promise-Like

JavaScriptJavaScriptBeginner
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Introduction

In this lab, we will explore the concept of Promises in JavaScript and learn how to identify if an object is Promise-like using the isPromiseLike function. Through practical examples, we will understand how Promises work and how to leverage them for asynchronous programming. By the end of this lab, you will have a solid understanding of Promises and how to identify them in your code.

Skills Graph

%%%%{init: {'theme':'neutral'}}%%%% flowchart RL javascript(("`JavaScript`")) -.-> javascript/BasicConceptsGroup(["`Basic Concepts`"]) javascript(("`JavaScript`")) -.-> javascript/AdvancedConceptsGroup(["`Advanced Concepts`"]) javascript/BasicConceptsGroup -.-> javascript/variables("`Variables`") javascript/BasicConceptsGroup -.-> javascript/data_types("`Data Types`") javascript/BasicConceptsGroup -.-> javascript/arith_ops("`Arithmetic Operators`") javascript/BasicConceptsGroup -.-> javascript/comp_ops("`Comparison Operators`") javascript/BasicConceptsGroup -.-> javascript/functions("`Functions`") javascript/BasicConceptsGroup -.-> javascript/obj_manip("`Object Manipulation`") javascript/AdvancedConceptsGroup -.-> javascript/closures("`Closures`") subgraph Lab Skills javascript/variables -.-> lab-28439{{"`Value Is Promise-Like`"}} javascript/data_types -.-> lab-28439{{"`Value Is Promise-Like`"}} javascript/arith_ops -.-> lab-28439{{"`Value Is Promise-Like`"}} javascript/comp_ops -.-> lab-28439{{"`Value Is Promise-Like`"}} javascript/functions -.-> lab-28439{{"`Value Is Promise-Like`"}} javascript/obj_manip -.-> lab-28439{{"`Value Is Promise-Like`"}} javascript/closures -.-> lab-28439{{"`Value Is Promise-Like`"}} end

JavaScript Promises

To check if an object is similar to a Promise, use the function isPromiseLike. This function checks if the object is not null, has a type of object or function, and has a .then property that is also a function.

Here is the code for isPromiseLike:

const isPromiseLike = (obj) =>
  obj !== null &&
  (typeof obj === "object" || typeof obj === "function") &&
  typeof obj.then === "function";

Here are some examples of how to use isPromiseLike:

isPromiseLike({
  then: function () {
    return "";
  }
}); // true

isPromiseLike(null); // false

isPromiseLike({}); // false

To start practicing coding in JavaScript, open the Terminal/SSH and type node.

Summary

Congratulations! You have completed the Value Is Promise-Like lab. You can practice more labs in LabEx to improve your skills.

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