Pol's Coding Notes

# Front-End Interview

# Random notes

  • flex-grow: number defines the space each flex element occupies. If not written manually, it is set to 1, so all the items occupy the same fraction of space.
  • Decorative images should always have an empty alt attribute
  • alt attribute in images is really important for SEO purposes
  • Cache busting is to force the browser to download new files that may have been stored on the client side. Can be done by appending ?=v2 to the script in our file, for example
  • @media properties -> all, screen, print, speech
  • Primitives (strings and numbers) are compared by their value, while objects are compared by their reference (location in memory)
  • XSS is a cross-site scripting attack. The attacker injects malicious code to our site, client-side. To prevent it:
    1. use textContent instead of innerHTML
    2. escape HTML tags on the server
  • About JS expressions and statements ->

    • If you can print it or assign it to a variable, itā€™s an expression. If you canā€™t, itā€™s a statement.

  • 6 FALSY VALUES: NaN, 0, undefined, false, '', null
  • Semicolons are not required in Javascript, only in some edge cases. The interpreter will add them automatically.
  • HOISTING:

    • No matter where functions and variables are declared, they are moved to the top of their scope regardless of whether their scope is global or local.

  • JS ASI: Automatic Semicolon Insertion that can lead to bugs.
  • Difference between defer and async in a <script> tag:

    • The defer attribute downloads the script while the document is still parsing but waits until the document has finished parsing before executing it.

    • The async attribute downloads the script during parsing the document but will pause the parser to execute the script before it has fully finished parsing.

  • rel="noopener" prevents opened links from manipulating the source page. Should always put in <a> tags.
  • Javascript data types:
    • Primitive
      1. Boolean
      2. Null
      3. Undefined
      4. Number
      5. String
      6. Symbol (newly added)
    • Non-primitive
      1. Object
      • Array
      • Date
      • function
  • The Object.create() method creates a new object, using an existing object to provide the newly created object's __proto__.
  • The Promise object represents the eventual completion (or failure) of an asynchronous operation, and its resulting value.
  • Difference between null and undefined -> undefined is used when the nothing is not known, and null is used when the nothing is known.
  • CSS specificity:
    • Value matrix: [inline, id, class/pseudo-class/attribute, tag/pseudo-element]
    • In cases of equal specificity, the last rule is applied
  • Storing data in a user's browser. Before it was done with cookies, but these methods are faster and allow more size (5mb)
    1. localStorage
    • Data is permanent
    1. sessionStorage
    • When the user closes window or tab, the data is deleted

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