JS counts the number of occurrences of each letter in a string

1. Realize the number of occurrences of each letter in a JS statistical string in a conventional way

//创建一个空对象，目的：把字母作为键，次数作为值
function countStr(str) {
    
    
	var obj = {
    
    };//创建一个空对象
	for (var i = 0; i < str.length; i++) {
    
    //遍历字符串,获得每个字母
		var key = str[i];//每个字母
        if (obj[key]) {
    
    
          obj[key]++;//判断obj中有没有这个键
        } else {
    
    
          //对象中没有这个字母，那就把字母加到对象中，并且给这个字母一个出现的次数，默认一次
          obj[key] = 1;//此时会把每个字母变成属性，并赋予属性值1
        }
      }
      //遍历对象，显示每个字母的次数
	for (var key in obj) {
    
    
		console.log(key + "出现了" + obj[key] + "次");
	}
}

Effect:

Two, one line of code realizes the number of occurrences of each letter in the JS statistical string

function countStr(str){
    
    
	return [...str].reduce((a,b)=>(a[b]?a[b]++:a[b]=1,a),{
    
    });
}

This method is more convenient, and the returned result is an Object object:

3. Summary

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