需求 'get-element-by-id' 變?yōu)?'getElementById'

let str = 'get-element-by-id'; 
function firstLetterToUpper(str) {
    return str.charAt(0).toUpperCase() + str.substring(1, str.length)
}


// 
function convertToCamel(str) {
    let strArr = str.split('-');
    return strArr.map((item, key) => {
        if (!key) return item
        return firstLetterToUpper(item)
    }).join('')
}


let result = convertToCamel(str);   // getElementById