English Quiz - this, flex/grid, null/undefined

1. Describe what 'this' is in JavaScrtipt.

• this is a self reference variable. this points the object including itself or the object creating an instance.
• this binding is connecting between this and object pointed by this.
• this is determined by how a function is called (runtime binding).
  • when normal function calls, this points global variable, window.
  • when method of a object calls, this points the object which call the method.
  • when the constructor function of a class calls, this points the instance made by the constructor funtion.
  • when function prototype methods call, apply, bind calls, this point the first argument which the function get.

2. Have you played around with the new CSS Flexbox or Grid specs? What's good about it?

• yes, I have.
• the flex box is good about the ablity to align and justify items horizontally or vitically in 1-Dimention. and the flex box can shrink or stretch an item in flex box.
• the grid is good about align items in 2-Dimention(coulmns and rows). grid can position items in difficult arragnment.

3. What is the difference between ‘null’ and ‘undefined’? Please elaborate your answer with some examples.

• 'null' value represents the intentional absence of any object value. It is commonly used to indicate that a variable or object property does not have a value.
• 'undefined' is primitive value that is automatically assigned to variables that have been declared but have not been assigned a value.

참고

• MDN - this
• MDN - Basic concepts of flexbox
• MDN - CSS Grid Layout
• MDN - null