In JavaScript, the value of this is determined by how a function is called
A function's this references the execution context for that call, determined entirely by how the function was called.
A this-aware function can thus have a different context each time it's called, which makes it more flexible & reusable.
Refere to the object which invoke it
let work = {
teacher: "Sarah",
ask(q){
console.log(this.teacher,q)
}
}
// work call ask
work.ask("Why?")
// Sarah Why?function ask(q){
console.log(this.teacher,q)
}
let work1 = {
teacher: "Sarah1",
ask:ask
}
let work2 = {
teacher: "Sarah2",
ask:ask
}
work1.ask("Why?")
// Sarah1 Why?
work2.ask("Why?")the same as prevous but i explictly send this
function ask(q){
console.log(this.teacher,q)
}
let work1 = {
teacher: "Sarah1"
}
let work2 = {
teacher: "Sarah2"
}
ask.call(work1,"Why?")
// Sarah1 Why?
ask.call(work2,"Why?")
// Sarah2 Why?Hard binding locks a function's this context to a fixed object, ensuring predictability and preventing accidental changes.
let work = {
teacher: "Sarah",
ask(q){
console.log(this.teacher,q)
}
}
setTimeout(work.ask,3000) // undefined
// you are passing the method reference without binding it to the work object
//Therefore, when the ask method is executed after the timeoutfunction ask(q){
console.log(this.teacher, q)
}
const n = new ask("Why?")
n //undefined Why? - Create a brand new empty object
- Link that object to another object
- Call function with this set to the new object
- If function does not return an object, assume return of this
Thes steps will happen if calling new with empty fun
refer to the globle window or obj
// this works in the browsre console
const t = "Sarah";
function ask(q) {
console.log(this.t, q);
}
ask("Why?");
// this refer to the globale obj which has tuse “use strict”
-
Is the function called by new? >>
this will be the newly created obj -
Is the function called by call() or apply()?
Note: bind() effectively uses apply() -
Is the function called on a context object? >>
the object -
DEFAULT: global object (except strict mode) >>
global object
- arrow fun don’t define a this keyword
- if you put this keyword inside an arrow fun it behave like any other varible, so it will sreach in the outer scope and use it’s this (it will work lexically)
- using new with arrow fun fire an error
- objects are not scope, ex:
const work = {
teacher: "Sarah",
ask: q=>{
console.log(this.teacher, q)
}
}
work.ask("Why") // undefined Why
// work is not a scope, so the scope of this is the globale scopeOnly use => arrow functions when you need exical this.
Regular expressions are used in programming languages to match parts of strings. You create patterns to help you do that matching.
/*
If you want to find the word the in the string The dog chased the cat,
you could use the following regular expression:
*/
let testStr = "freeCodeCamp";
let testRegex = /Code/;
testRegex.test(testStr);if at least 0ne accure it will be true
let petString = "James has a pet fish.";
let petRegex = /dog|cat|bird|fish/;
let result = petRegex.test(petString);
console.log(result) // trueYou can match both cases using what is called a flag. There are other flags but here you'll focus on the flag that ignores case - the i flag.
// /ignorecase/i. This regex can match the strings ignorecase,
// igNoreCase, and IgnoreCase.
let myString = "freeCodeCamp";
let fccRegex = /freeCodeCamp/i; // Change this line
let result = fccRegex.test(myString); // trueextract the actual matches you found with the .match() method.
Note that the .match syntax is the "opposite" of the .test method you have been using thus far:
"Hello, World!".match(/Hello/);
let ourStr = "Regular expressions";
let ourRegex = /expressions/;
console.log(ourStr.match(ourRegex))
/*
[
'expressions',
index: 8,
input: 'Regular expressions',
groups: undefined
]
*/you can use the global search flag: g.
let testStr = "Repeat, Repeat, Repeat";
let repeatRegex = /Repeat/g;
testStr.match(repeatRegex);
//["Repeat", "Repeat", "Repeat"]You can have multiple flags on your regex like
/search/gi
. will match any one character.
/*
Complete the regex unRegex so that it matches the strings
run, sun, fun, pun, nun, and bun.
*/
let exampleStr = "Let's have fun with regular expressions!";
let unRegex = /.un/; // Change this line
let result = unRegex.test(exampleStr);bag, big, and bug but not bog. You can create the regex /b[aiu]g/
let bigStr = "big";
let bagStr = "bag";
let bugStr = "bug";
let bogStr = "bog";
bigStr.match(bgRegex);
bagStr.match(bgRegex);
bugStr.match(bgRegex);
// insted we can make
let bgRegex = /b[aiu]g/;
bogStr.match(bgRegex);let catStr = "cat";
let batStr = "bat";
let matStr = "mat";
let bgRegex = /[a-e]at/;
catStr.match(bgRegex);
batStr.match(bgRegex);
matStr.match(bgRegex);
/ *
[
'T', 'h', 'e', 'q', 'u', 'i', 'c',
'k', 'b', 'r', 'o', 'w', 'n', 'f',
'o', 'x', 'j', 'u', 'm', 'p', 's',
'o', 'v', 'e', 'r', 't', 'h', 'e',
'l', 'a', 'z', 'y', 'd', 'o', 'g'
]
*/For example, /[0-5]/ matches any number between 0 and 5, including the 0 and 5.
//possible to combine a range of letters and numbers in a single character
let jennyStr = "Jenny8675309";
let myRegex = /[a-z0-9]/ig;
jennyStr.match(myRegex);
/*
[
'J', 'e', 'n', 'n',
'y', '8', '6', '7',
'5', '3', '0', '9'
]
*/My solution:
let myString = "Hello, World!";
let myRegex = /Hello/;
let result = myRegex.test(myString)My solution:
let waldoIsHiding = "Somewhere Waldo is hiding in this text.";
let waldoRegex = /Waldo/; // Change this line
let result = waldoRegex.test(waldoIsHiding);My solution:
let petString = "James has a pet cat.";
let petRegex = /dog|cat|bird|fish/; // Change this line
let result = petRegex.test(petString);My solution:
let myString = "freeCodeCamp";
let fccRegex = /freeCodeCamp/i; // Change this line
let result = fccRegex.test(myString);My solution:
let extractStr = "Extract the word 'coding' from this string.";
let codingRegex = /coding/; // Change this line
let result = extractStr.match(codingRegex); // Change this lineMy solution:
let twinkleStar = "Twinkle, twinkle, little star";
let starRegex = /Twinkle/gi; // Change this line
let result = twinkleStar.match(starRegex); // Change this lineMy solution:
let exampleStr = "Let's have fun with regular expressions!";
let unRegex = /.un/; // Change this line
let result = unRegex.test(exampleStr);My solution:
let quoteSample = "Beware of bugs in the above code; I have only proved it correct, not tried it.";
let vowelRegex = /[aeiou]/ig; // Change this line
let result = quoteSample.match(vowelRegex); // Change this lineMy solution:
let quoteSample = "The quick brown fox jumps over the lazy dog.";
let alphabetRegex = /[a-z]/ig; // Change this line
let result = quoteSample.match(alphabetRegex); // Change this lineMy solution:
let quoteSample = "Blueberry 3.141592653s are delicious.";
let myRegex = /[h-s2-6]/ig; // Change this line
let result = quoteSample.match(myRegex); // Change this lineMy solution:
const twoArePositive = (a, b, c)=> {return [a,b,c].filter(i=>i>0).length===2}My solution:
function getCellAddresses(range) {
const letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
const ans = [], [start, end] = range.split(":")
if (start === end)return []
for (let i = parseInt(start.slice(1)); i <= parseInt(end.slice(1)); i++) {
const col = []
for (let j = letters.indexOf(start[0]); j <= letters.indexOf(end[0]); j++) {
col.push(letters[j] + i)
}
ans.push(...col)
}
return ans
}My solution:
function count(sring) {
let ans = {}
for (let i of sring)
ans[i] = ans[i] === undefined ? 1 : ans[i] +1
return ans;
}