Realize pyramids through JS (asterisk pyramid, palindrome symmetric digital pyramid)

Take a look at the implementation effect first ：

Every time I see something like this that needs to implement graphics , The first step is to find the law of graphics .
Start with the law ！
Seeing and deciding this figure requires spaces and ’'.
From the top down , The number of stars is ：1,3,5,7,9,11…
The number of spaces is ：9 8 7 6 5 4 3 2 1 0
Then the law of stars is 2n-1 , Space is decreasing every layer 1
But through js To achieve , You need to start from the array （ The pyramids ） Index and length of the angle to write their rules ,
Then the stars are ： 2（ Index value +1）-1 ,
And the space is ： Height - Index value .
After knowing the rules , Add a string ：str.repeat(n) We can realize the digital pyramid ~
The code is as follows ：

function tar(n){
    for(let i=0;i<n;i++){
      let str1=' '
      let str2 = str1.repeat(n-i)
      let str3='*'
      let str4 = str3.repeat(2*(i+1)-1)
      console.log(str2+str4)
    }
}

call ：

tar(10)

Achieve results ：

In fact, the code is very simple , Don't understand why others don't str.repeat, So easy hhhhh

Advanced ： Make a pyramid of palindrome numbers . Right and left symmetry

Let's look at the implementation results first ：

ha-ha , In fact, the soup is not changed Or continue to find rules
n=0 yes 1 n=1 yes 121 n=2 yes 12321
Since it's palindrome , Just write one side , On the other side, through the array method (reverse) That's all right. , Convert to string splicing .
So the simplification is
n=0 yes 1 n=1 yes 12 n=2 yes 123
Implementation code ：

//  Realize palindrome number 
function countNum(n){
    let arr=[]
    for(let i=0;i<n;i++){
        arr.push(i+1)
    }
    let str = arr.join("")
    let arr1 = str.split("").reverse()
    arr1.shift()
    let str1 = arr1.join("")
    return str+str1
}
// Main code 
function tar(n){
    for(let i=0;i<n;i++){
      let str1=' '
      let str2 = str1.repeat(n-i)
      let str3 = countNum(i+1)
      console.log(str2+str3)
    }
}

call ：

tar(9)

The implementation result is shown in the figure above , Successful implementation ~ Very simple, actually . I didn't read the code written by others , It's not the optimal solution , But this can help a front end be more proficient in using strings , Array method , And the flexible application of the conversion between the two , Strengthen the memory .