javascript - 具有现代 ES6 javascript 类的方法的局部临时变量

Question

在旧式 javascript 类中，您可以使用 IIFE为方法定义一些临时变量，这些变量是预先分配的，因此不必在每次调用方法时都调用 new。

// constructor
var MyClass = function(x,y,z){ this.pos=new vec3(x,y,z); } 

// method
MyClass.prototype.vec_combine = ( function( a,b,c, up,fw) {
    var side = new vec3(); // allocated at construction, not at invocation
    return function vec_combine( a,b,c, up,fw) { 
       cross_product( up,fw, side ); // side is perpendicular to up,fw
       side.normalize();
       this.pos.x = fw.x*a + up.x*b + side.x*c;
       this.pos.y = fw.y*a + up.y*b + side.y*c;
       this.pos.z = fw.z*a + up.z*b + side.z*c; 
    }
}() );

如何使用类似现代 ES6 的类来做到这一点？

class MyClass{
  constructor(x,y,z){ this.pos=new vec3(x,y,z); } 

  // method
  vec_combine( a,b,c, up,fw) {
    var side = new vec3(); // I don't want do "new" each invocation
    cross_product( up,fw, side ); // side is perpendicular to up,fw
    side.normalize();
       this.pos.x = fw.x*a + up.x*b + side.x*c;
       this.pos.y = fw.y*a + up.y*b + side.y*c;
       this.pos.z = fw.z*a + up.z*b + side.z*c; 
  }
}

Answer 1

你不能按照你的要求去做。

但是，如果您已经在使用 ES6，那么您很可能正在使用模块。您也可以在模块中有一个未导出的变量。

// Not exported
var side = new vec3(); // I don't want do "new" each invocation

export class MyClass{
  constructor(x,y,z){ this.pos=new vec3(x,y,z); } 

  // method
  vec_combine( a,b,c, up,fw) {
    cross_product( up,fw, side ); // side is perpendicular to up,fw
    side.normalize();
    this.pos.x = fw.x*a + up.x*b + side.x*c;
    this.pos.y = fw.y*a + up.y*b + side.y*c;
    this.pos.z = fw.z*a + up.z*b + side.z*c; 
  }
}

如果你不使用模块，你可以把整个类放在一个 IIFE 中

const MyClass =  (() => {
  var side = new vec3(); // I don't want do "new" each invocation

  return class {
    constructor(x,y,z){ this.pos=new vec3(x,y,z); } 

    vec_combine( a,b,c, up,fw) {
      cross_product( up,fw, side ); // side is perpendicular to up,fw
      side.normalize();
      this.pos.x = fw.x*a + up.x*b + side.x*c;
      this.pos.y = fw.y*a + up.y*b + side.y*c;
      this.pos.z = fw.z*a + up.z*b + side.z*c; 
    }
  }

});