How to use the caffeine-script-runtime.exists function in caffeine-script-runtime

argumentNames: function() {
          let cafBase;
          return Caf.exists(cafBase = this.arguments) &&
            cafBase.argumentNames || [];
        },
        childrenToUpdateScope: function() {

stnProps: function() {
                let base;
                return {
                  operand: (this.prefix || this.postfix).toString(),
                  tail: !!(Caf.exists((base = this.postfix)) && base.toString())
                };
              }
            }

this.prototype.toJs = function() {
        let identierString, cafBase;
        return this.value && this.key.isIdentifier
          ? (identierString = this.key.toJs()).match(/['"`]/)
              ? `${Caf.toString(
                  this.value.toJsExpressionWithParens()
                )}[${Caf.toString(identierString)}]`
              : `${Caf.toString(
                  this.value.toJsExpressionWithParens({ dotBase: true })
                )}.${Caf.toString(identierString)}`
          : `${Caf.toString(
              Caf.exists(cafBase = this.value) &&
                cafBase.toJsExpressionWithParens() ||
                ""
            )}[${Caf.toString(this.key.toJsExpression())}]`;
      };
    }

sourceFile: function() {
              let temp, base;
              return (temp =
                Caf.exists((base = this.parseTreeNode)) && base.sourceFile) !=
                null
                ? temp
                : "caffeine-script";
            }
          });

this.prototype.updateScope = function(scope) {
          let base;
          this.scope = scope;
          if (this.props.identifierHandle) {
            this.scope.addUniqueIdentifierHandle(this.props.identifierHandle);
          } else {
            if (
              !(Caf.exists((base = this.identifier)) && base.isUniqueIdentifier)
            ) {
              this.scope.addIdentifierUsed(this.propName);
            }
          }
          return instanceSuper.updateScope.apply(this, arguments);
        };
        this.getter({