typescript best way to know if variable is not undefined or null code example

Example 1: check if variable is undefined or null jquery

if (variable == null) {
    // variable is either null or undefined
}

Example 2: javascript check if null

if (variable === null) { //Executes only if variable is null but not undefined
  //Code here
}

if (variable == null) { //Executes if variable is null OR undefined
  //Code here
}