code: function isUseStrictPrologueDirective(node) {
              var nodeText = ts.getTextOfNodeFromSourceText(file.text, node.expression);
              // Note: the node text must be exactly "use strict" or 'use strict'.  It is not ok for the
              // string to contain unicode escapes (as per ES5).
              return nodeText === '"use strict"' || nodeText === "'use strict'";
          }
docs: / Should be called only on prologue directives (isPrologueDirective(node) should be true)