連想配列の値からインデックスを取得する

const obj = [
    { num: 0, name: 'AAA', age: '60'},
    { num: 1, name: 'BBB', age: '20'},
    { num: 2, name: 'CCC', age: '40'},
    { num: 3, name: 'DDD', age: '50'},
];
obj.findIndex(({name}) => name === 'DDD'); // 3
obj.findIndex(({age}) => age === '20');    // 1

const obj = {
    key1: 'AAA',
    key2: 'BBB',
    key3: 'CCC',
    key4: 'DDD'
};
var find_value = 'DDD';
const keys = Object.keys(obj);
for (let i=0; i < keys.length; i++) {
    let key = keys[i];
    let val = obj[key];
    if (val == find_value) {
        console.log('index = ' + String(i));　　// 3
        break;
    }
}