<span>var</span> simpleDurationStringToMillis = <span><span>function</span>(<span>str</span>) </span>{
    <span>if</span> (!str) {
        <span>return</span> <span>0</span>;
    }
    <span>var</span> answer = <span>0</span>;
    <span>var</span> millisBySymbol = {
        <span>'ms'</span>: <span>1</span>,
        <span>'s'</span>: <span>1000</span>,
        <span>'m'</span>: <span>60</span> * <span>1000</span>,
        <span>'h'</span>: <span>60</span> * <span>60</span> * <span>1000</span>,
        <span>'d'</span>: <span>24</span> * <span>60</span> * <span>60</span> * <span>1000</span>,
        <span>'w'</span>: <span>7</span> * <span>24</span> * <span>60</span> * <span>60</span> * <span>1000</span>,
        <span>'M'</span>: <span>30</span> * <span>24</span> * <span>60</span> * <span>60</span> * <span>1000</span>,
        <span>'y'</span>: <span>365</span> * <span>24</span> * <span>60</span> * <span>60</span> * <span>1000</span>
    };
    <span>var</span> <span>number</span> = <span>''</span>;
    <span>for</span> (<span>var</span> i = <span>0</span>; i &lt; str.length; ++i) {
        <span>if</span> (i &gt;= <span>'0'</span> &amp;&amp; str[i] &lt;= <span>'9'</span>) {
            <span>number</span> += str[i];
        } <span>else</span> {
            <span>var</span> symbol = str[i];
            <span>if</span> ((i + <span>1</span>) &lt; str.length) {
                <span>if</span>(str[i + <span>1</span>] &gt;= <span>'1'</span> &amp;&amp; str[i + <span>1</span>] &lt;= <span>'9'</span>) {
                    symbol += str[i + <span>1</span>];
                    ++i;
                }
            }
            <span>var</span> millis = millisBySymbol[symbol];
            <span>if</span> (millis &amp;&amp; <span>number</span>) {
                answer += <span>parseInt</span>(<span>number</span>, <span>10</span>) * millis;
                <span>number</span> = <span>''</span>;
            } <span>else</span> {
                answer = <span>-1</span>;
                <span>break</span>;
            }
        }
    }
    <span>return</span> answer;
}

console.log(simpleDurationStringToMillis('0'));
console.log(simpleDurationStringToMillis('1ms'));
console.log(simpleDurationStringToMillis('10s'));
console.log(simpleDurationStringToMillis('100m'));
console.log(simpleDurationStringToMillis('1000h'));
console.log(simpleDurationStringToMillis('10000d'));
console.log(simpleDurationStringToMillis('1000000w'));
console.log(simpleDurationStringToMillis('10000000M'));
console.log(simpleDurationStringToMillis('100000000y'));
console.log(simpleDurationStringToMillis('a'));
console.log(simpleDurationStringToMillis('12a'));
console.log(simpleDurationStringToMillis('3mss'));

0
1
10000
6000000
3600000000
864000000000
604800000000000
25920000000000000
3153600000000000000
-1
-1
-1