ASI

JavaScript automatically inserts semicolons (;) in certain cases, but not always. Understanding ASI is critical to avoid subtle bugs. Also, it is great to make unique payloads to bypass restrictions. Here are the key rules, remember them for future reference:

When ASI Adds Semicolons

• At the End of a File

• After a Line Break (if the next line is invalid syntax)

  • let x = 1  // ASI adds `;`
    let y = 2  // ASI adds `;`

• before }, continue, break, return, throw, or yield

  • {let x=1}{let x=3}{let x=null}

When ASI Does Not Add Semicolons

• If the next line starts with (, [, `, /, +, or -

• After ++ or --

• In for Loops