Nashornでletとconstを使う

1. Nashornのバージョンを確認する

>echo "quit();" | jjs -version

nashorn 1.8.0_66

jjs> quit();

jjs>

>

2. 実行するスクリプト(LetAndConst.js):

try {

    const CONST_VALUE = 100;

    print("CONST_VALUE=${CONST_VALUE}");

    try {

        CONST_VALUE = 200;

    } catch (e) {

        print(e);

    }

    let letValue = CONST_VALUE + 1;

    print("letValue=${letValue}");

    var varValue = letValue + 1;

    print("varValue=${varValue}");

} finally {

    print("typeof CONST_VALUE: " + typeof CONST_VALUE);

    print("typeof letValue: " + typeof letValue);

    print("typeof varValue: " + typeof varValue);

}

3. jjsで実行する(--language=es6オプションが無いので文法エラーが起きた):

>jjs -scripting -fullversion LetAndConst.js

nashorn full version 1.8.0_66-b18

LetAndConst.js:2:1 Expected an operand but found const

    const CONST_VALUE = 100;

    ^

LetAndConst.js:9:5 Expected ; but found letValue

    let letValue = CONST_VALUE + 1;

        ^

LetAndConst.js:13:0 Expected eof but found }

} finally {

^




4. jjsで実行する(--language=es6オプションが有るので実行された):

>jjs -scripting -fullversion --language=es6 LetAndConst.js

nashorn full version 1.8.0_66-b18

CONST_VALUE=100

TypeError: Assignment to constant "CONST_VALUE"

letValue=101

varValue=102

typeof CONST_VALUE: undefined

typeof letValue: undefined

typeof varValue: number