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JavaScript: eval function

eval(expr_or_stmt) evaluates the string expr_or_stmt (which probably should be an expression or a sequence of statements).

It returns the value of the expression or the last statement.

The eval function is function that is defined in the global object.

<!DOCTYPE html>
<html>
<head>
  <meta content="text/html;charset=utf-8" http-equiv="Content-Type">
  <title>eval</title>

  <script type="text/javascript">

    var table_, tbody_;

    function eval_string(str) {
      var tr      = document.createElement('tr');
      var td_str  = document.createElement('td');
      var td_eq   = document.createElement('td');
      var td_eval = document.createElement('td');

      td_str .appendChild(document.createTextNode(     str ));
      td_eq  .appendChild(document.createTextNode(     '=' ));
      td_eval.appendChild(document.createTextNode(eval(str)));

      tr.appendChild(td_str );
      tr.appendChild(td_eq  );
      tr.appendChild(td_eval);

      tbody_.appendChild(tr);
      
    }
    
    function main() {
      
      table_ = document.createElement('table');
      tbody_ = document.createElement('tbody');

      table_.appendChild(tbody_);

      document.getElementsByTagName('body')[0].appendChild(table_);

      eval_string("42"                      );
      eval_string("21 * 2"                  );
      eval_string("Boolean( 0)"             );
      eval_string("Boolean(42)"             );
      eval_string("eval(eval(40 + '+' + 2))");
      eval_string("typeof(Boolean(42))     ");
      eval_string("typeof(table_)          ");
    }

  </script>

</head>
<body onload='main()';>
</body>
</html>

Github repository about-javascript, path: /objects/Global-Object/function-properties/eval.html

JavaScript: eval function

See also