Cheat sheet

Sure! Here’s a concise JavaScript cheatsheet that covers the basics and some commonly used features.

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JavaScript Cheatsheet

1. Variables

• Declaration:

    var name = "Alice"; // Old way, function/global scoped
    let age = 25;       // Block scoped, can be reassigned
    const pi = 3.14;   // Block scoped, cannot be reassigned
  

2. Data Types

• Primitive Types:

  • String: "Hello"

  • Number: 42, 3.14

  • Boolean: true, false

  • Null: null

  • Undefined: undefined

  • Symbol: Symbol('description')

  • BigInt: 123n

• Reference Types:

  • Object:

      let person = { name: "Alice", age: 25 };
    

  • Array:

      let fruits = ["apple", "banana", "cherry"];
    

3. Operators

• Arithmetic: +, -, *, /, % (modulus)

• Assignment: =, +=, -=, *=, /=

• Comparison: ==, === (strict), !=, !== (strict), <, >, <=, >=

• Logical: && (and), || (or), ! (not)

4. Control Flow

• Conditional Statements:

    if (condition) {
        // code
    } else if (anotherCondition) {
        // code
    } else {
        // code
    }
  

• Switch Statement:

    switch (expression) {
        case value1:
            // code
            break;
        case value2:
            // code
            break;
        default:
            // code
    }
  

• Loops:

  • For Loop:

      for (let i = 0; i < 5; i++) {
          console.log(i);
      }
    

  • While Loop:

      let i = 0;
      while (i < 5) {
          console.log(i);
          i++;
      }
    

  • Do-While Loop:

      let j = 0;
      do {
          console.log(j);
          j++;
      } while (j < 5);
    

5. Functions

• Function Declaration:

    function greet(name) {
        return "Hello, " + name;
    }
  

• Function Expression:

    const add = function(a, b) {
        return a + b;
    };
  

• Arrow Function:

    const multiply = (a, b) => a * b;
  

6. Objects and Arrays

• Creating an Object:

    let car = {
        make: "Toyota",
        model: "Camry",
        year: 2020
    };
  

• Accessing Object Properties:

    console.log(car.make); // Dot notation
    console.log(car["model"]); // Bracket notation
  

• Creating an Array:

    let colors = ["red", "green", "blue"];
  

• Accessing Array Elements:

    console.log(colors[0]); // Output: red
  

• Array Methods:

    colors.push("yellow"); // Add to end
    colors.pop();          // Remove from end
    colors.shift();        // Remove from start
    colors.unshift("purple"); // Add to start
  

7. ES6 Features

• Template Literals:

    let name = "Alice";
    let greeting = `Hello, ${name}!`; // Template string
  

• Destructuring Assignment:

    let person = { name: "Alice", age: 25 };
    let { name, age } = person; // Destructure properties
  

• Spread Operator:

    let arr1 = [1, 2, 3];
    let arr2 = [...arr1, 4, 5]; // Copy and add elements
  

• Rest Parameters:

    function sum(...numbers) {
        return numbers.reduce((a, b) => a + b, 0);
    }
  

8. Error Handling

• Try...Catch:

    try {
        // code that may throw an error
    } catch (error) {
        console.error(error); // Handle error
    }
  

9. DOM Manipulation

• Select Elements:

    let element = document.getElementById("myId");
    let elements = document.querySelectorAll(".myClass");
  

• Modify Elements:

    element.textContent = "New text"; // Change text
    element.style.color = "blue"; // Change style
  

• Event Handling:

    element.addEventListener("click", function() {
        alert("Element clicked!");
    });
  

10. Common Array Methods

• forEach:

    arr.forEach(item => {
        console.log(item);
    });
  

• map:

    let doubled = arr.map(x => x * 2);
  

• filter:

    let evens = arr.filter(x => x % 2 === 0);
  

• reduce:

    let sum = arr.reduce((total, num) => total + num, 0);
  

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Conclusion

This cheatsheet provides a quick overview of JavaScript essentials. For more complex topics or deeper learning, consider exploring specific areas in more detail. If you need any further explanation or examples, feel free to ask!