What JS? Itself
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The document discusses key concepts about JavaScript including: - JavaScript was created in 10 days by Brendan Eich. - It is loosely typed, weakly typed, and forgiving with syntax like optional semicolons. - Variables can contain different types and operations between types perform conversions. - Conditionals should always use triple equals (===) for comparisons. - Type conversions occur behind the scenes which can lead to unexpected results. - Scopes determine where variables are stored and found, with inner scopes having access to outer scopes.
![Type object
var dogs = [];
if (dogs) // Object
actually exist
dogs.push(“Terry”); // Now has one
element
console.log(dogs); // Prints [“Terry”]
If (dogs.length) // Length won’t be
zero
console.log(“Array has elements”); // So this actually prints](https://image.slidesharecdn.com/whatjsitself-170323211311/85/What-JS-Itself-22-320.jpg)
![Conditionals
// From `if (typeof aName == “string” && aName != “”)`
// To
if (aName) {
console.log(“Say hello to ” + aName);
}
Simplicity is on our side. Take that [INSERT CORRECT STARS
WAR CHARACTER]!](https://image.slidesharecdn.com/whatjsitself-170323211311/85/What-JS-Itself-28-320.jpg)
What JS? Itself
- 1. What JavaScript? Remove your whats of JavaScript
- 2. The Creation
- 3. Brendan Eich
- 4. Made JavaScript in 10 days. Hence..
- 6. It really doesn’t care Semicolons are optional Parameters may or may not be passed
- 7. It really doesn’t care function getMessage(message) { internalVariable = “The message is: ” return internalVariable + message } var result = getMessage(“dogs are nice”, 123, undefined, “etc”) console.log( result ) // this’d positively print “The message is: dogs are nice” without errors
- 8. It really doesn’t care Order of execution isn’t the order written
- 9. It really doesn’t care doSomething() function doSomething() { console.log( ‘doing something’ ) } // This do works..
- 10. Weakly typed All variables may contain anything.
- 11. var something = 5; console.log(something); // shows a 5 function sayHi() { return “Hi!”; } something = sayHi(); console.log(something); // shows hi! Weakly typed
- 12. Weakly typed Operations between types can be executed Conversion on the fly will occur
- 13. Weakly typed var firstValue = 0; firstValue++; // increase the integer console.log(firstValue); // shows 1 firstValue += “1”; // concatenates 1 with “1” console.log(firstValue); // shows “11”
- 16. Type undefined People say that undefined may change the value. I don’t care about that. if (newVariable === undefined) This is perfectly fine for my standards. (function(undefined) { console.log(undefined); // Prints the given string, my own undefined })(“my own undefined”); This is stupid. So I don’t care about undefined not being undefined.
- 17. Type null Very common value in other languages. Can be seen a lot retrieving data from APIs. var received = null; if (received === null) {} // True if (!received) {} // True too
- 18. Type boolean var that = true; if (that === true) {} // This is silly if (that) {} // This is better if (that == false) {} // Same as the first, silly if (!that) {} // This is great
- 19. Type string var text = “There was a time”; if (text != “”) console.log(“Text is not empty”); // Above code is far too silly, it can be simpler as below if (text) console.log(“Text is not empty”);
- 20. Type number var luckNumber = 5; if (luckNumber != 0) console.log(“Number is not zero”); // This can be easier: if (luckNumber) console.log(“Number is positive or negative, not zero”);
- 21. Type object // Right way to initialize an object, not using new var virtualObject = {}; if (virtualObject) console.log(“Object exist”); // Even without attributes, it exist virtualObject.firstAttribute = 1234; // Add attribute if (virtualObject.unexistingMethod) // Continue only if method available virtualObject.unexistingMethod(); // Unknown method error prevented
- 22. Type object var dogs = []; if (dogs) // Object actually exist dogs.push(“Terry”); // Now has one element console.log(dogs); // Prints [“Terry”] If (dogs.length) // Length won’t be zero console.log(“Array has elements”); // So this actually prints
- 24. Conditionals With or without brackets conditionals must be understood.
- 25. Conditionals if (typeof aName == “string” && aName != “”) { console.log(“Say hello to ” + aName); } This is wrong, javascript has a conditional of 3 equals. Do NEVER use the 2 equals. 2 sometimes are OK, 3 will be always OK. Use 3 equals always.
- 26. Conditionals if (typeof aName === “string” && aName !== “”) { console.log(“Say hello to ” + aName); } Now this is still pretty awful. If aName is integer 18 then you cannot print hello to 18.
- 27. Conditionals if (aName !== “”) { console.log(“Say hello to ” + aName); } Yet horrible, there is no need to ask for not empty string explicitly when it can be simpler.
- 28. Conditionals // From `if (typeof aName == “string” && aName != “”)` // To if (aName) { console.log(“Say hello to ” + aName); } Simplicity is on our side. Take that [INSERT CORRECT STARS WAR CHARACTER]!
- 29. Conditionals ALWAYS USE 3 EQUALS
- 30. Types Conversion Now we are entering to the fun side JavaScript is well known for its types conversion table Also for its logic tables And for everything else, but not in the good way More as a joke So lets try to get a good laugh from it
- 44. Scope We can define a scope as a set of rules for storing variables in some location, and for finding those variables at a later time.
- 45. Scope
- 46. Nested Scopes JavaScripts starts at the currently executing scope, looks for the variable there, then if not found, keeps going up one level, and so on. If the outermost global scope is reached, the search stops, whether it finds the variable or not.
- 47. Nested Scopes
Editor's Notes
- #2: TODO: put letter of code to code and mark comments in another color