regex101: PCRE2 (PHP) Match Workspace

Regular Expression

^Q: ((?:.*|\n)*?)\n*A: (.+(?:\n(?:^.{1,3}$|^.{4}(?<!<!--).*))*)

New

Q: diff between null and undefined?

A: Null indicates an intentional empty value. 
- Undefined indicates the total absence of a value. This happen when only the variable was declared without any initializer. A missing key in an object is also undefined. 
```javascript
export function ticketStatus(tickets, ticketId) {
  if (tickets[ticketId] === undefined) {
    return 'unknown ticket id';
  } else if (tickets[ticketId] === null) {
    return 'not sold';
  } else {

    return `sold to ${tickets[ticketId]}`;
  }
}
```
<!--ID: 1673953179724-->


---
Q: rewrite to use [[JS Object.assign]]
```javascript
visitor.ticketId = null;

return visitor;
```


A: Just pass only the props we want to overwrite to assign
```javascript
return Object.assign(visitor, {ticketId: null});
```
<!--ID: 1673953179746-->


---

Q: diff between isNaN() global vs Number.isNaN()?

A: global isNaN() does type conversion. 
- Since I am trying to test whether the string contains a valid number, this is the right choice. 
- If the input is already a number, then Number.isNaN() might be better. as

---

Substitution

Q: diff between null and undefined?

A: Null indicates an intentional empty value. 
- Undefined indicates the total absence of a value. This happen when only the variable was declared without any initializer. A missing key in an object is also undefined. 
```javascript
export function ticketStatus(tickets, ticketId) {
  if (tickets[ticketId] === undefined) {
    return 'unknown ticket id';
  } else if (tickets[ticketId] === null) {
    return 'not sold';
  } else {

    return `sold to ${tickets[ticketId]}`;
  }
}
```
<!--ID: 1673953179724-->


---
Q: rewrite to use [[JS Object.assign]]
```javascript
visitor.ticketId = null;

return visitor;
```


A: Just pass only the props we want to overwrite to assign
```javascript
return Object.assign(visitor, {ticketId: null});
```
<!--ID: 1673953179746-->


---

Q: diff between isNaN() global vs Number.isNaN()?

A: global isNaN() does type conversion. 
- Since I am trying to test whether the string contains a valid number, this is the right choice. 
- If the input is already a number, then Number.isNaN() might be better. as

---