TypeScript and array reduce function

Question

Do you know what the reduce array method does in JavaScript  Can you provide a simple example of usage  I searched on Google and the TypeScript language specification but could not find any decent explanation and examples

User · Answer

Just a note in addition to the other answers.

If an initial value is supplied to reduce then sometimes its type must be specified, viz:-

a.reduce(fn, [])

may have to be

a.reduce<string[]>(fn, [])

or

a.reduce(fn, <string[]>[])

User · Answer

Reduce   is     The reduce   method reduces the array to a single value  The reduce   method executes a provided function for each value of the array  from left-to-right   The return value of the function is stored in an accumulator  result total     It was         let array  1 2 3   function sum acc val   return acc val        gt  can change to  acc val   gt acc val let answer  array reduce sum      answer is 6   Change to      let array  1 2 3   let answer arrays reduce  acc val   gt acc val     Also you can use in    find max       let array  5 4 19 2 7       function findMax acc val             if val gt acc          acc val                     let biggest arrays reduce findMax      19    find an element that not repeated        arr    1  2  5  4  6  8  9  2  1  4  5  8  9      v   0     for i in range len arr        v   v   arr i      print value     6

User · Answer

It s actually the JavaScript array reduce function rather than being something specific to TypeScript   As described in the docs   Apply a function against an accumulator and each value of the array  from left-to-right  as to reduce it to a single value   Here s an example which sums up the values of an array    x000D   x000D  let total    0  1  2  3  reduce  accumulator  currentValue    gt  accumulator   currentValue   x000D  console log total   x000D   x000D   x000D    The snippet should produce 6

User · Answer

With TypeScript generics you can do something like this   class Person       constructor  public Name   string  public Age  number        var list   new Array lt Person gt     list push new Person  Baby   1    list push new Person  Toddler   2    list push new Person  Teen   14    list push new Person  Adult   25     var oldest person   list reduce   a  b    gt  a Age  gt  b Age   a   b    alert oldest person Name

[javascript] TypeScript and array reduce function

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