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JavaScript 字符串练习题之实现

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JavaScript 字符串练习题见这里


题 1:首字母改大写


function firstLetterToUpperCase(str) {
var res;
if (typeof str === 'string') {
res = str.charAt(0).toUpperCase() + str.substr(1);
} else {
res = str;
}
return res;
}

题 2:去字符串头尾空格


function trim(str) {
var res;
if (typeof str === 'string') {
res = str.replace(/^\s+/g, '')
.replace(/\s+$/g, '');
} else {
res = str;
}
return res;
}

题 3:将字符串中 _ 后面的小写字母变大写,并且删除 _


function toCamelStyle(str) {
var res;
if (typeof str === 'string') {
var isFisrstLetterUnderscore = str.charAt(0) === '_';
var wordArr;
if(isFisrstLetterUnderscore){
str = str.substr(1);
}
wordArr = str.split('_');
wordArr = wordArr.map(function (word, index) {
// firstLetterToUpperCase 在题目 1 中实现
return index === 0 ? word : firstLetterToUpperCase(word);
});
res = wordArr.join('');
if(isFisrstLetterUnderscore){
res = '_' + res;
}
} else {
res = str;
}
return res;
}

题 4:删除字符串中所有的数字


function removeNum(str) {
var res;
if (typeof str === 'string') {
res = str.replace(/\d/g, '');
} else {
res = str;
}
return res;
}

题 5: 反转字符串


function reverse(str) {
var res;
if (typeof str === 'string') {
res = [];
var charArr = str.split('');
var currIndex = charArr.length - 1;
for(; currIndex >= 0; currIndex--){
res.push(charArr[currIndex]);
}
res = res.join('');
} else {
res = str;
}
return res;
}

题 6: 统计字符串中各字符在字符串中出现的数量


function caculateExistNum(str) {
var res = false;
if (typeof str === 'string') {
res = {};
var charArr = str.split('');
charArr.forEach(function (eachChar) {
res[eachChar] = res[eachChar] ? res[eachChar] + 1 : 1;
});
}
return res;
}

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