What are the uses of '?' and '!' in Angular?

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? Used When checking whether the variable before the question mark is null or undefined, the program will not make an error.

  stu2: Student = {
    id: 1,
    name: undefined,
    age: 3
  };
  
<h1>stu2 name {{stu2!.name}}</h1>  // stu2 name 
<h1>stu2 id {{stu2!.id}}</h1>            // stu2 id 1

! Used to check that the program will not make an error when the variable after the exclamation mark is null or undefined.

stu3: Student;
 
<h1>stu3 id{{stu3?.id}}</h1>                // stu3 id
<h1>stu3 name{{stu3?.name}}</h1>      // stu3 name

For more programming-related knowledge, please visit: Introduction to Programming! !

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