如何克隆对象并迭代其中一个属性？

Question

I'm trying to clone an object within a promise and iterate a property of it.

This seems to work, you get an array of objest where page_num is incremented from 2 to 44.

var allOptions = _.map(_.range(2, 45), function(page){
  return { body: { action: 'read', page_num: page, page_size: 5 }}
})

Promise.map(allOptions, function(options){
  return Promise.resolve(options).delay(3000)
}).then(console.log)

However this example above is creating an object from scratch every time.

When I try to clone an existing object like so I get the behavior described below.

var masterOptions = { body: { action: 'read', page_num: 1, page_size: 5 }}

var allOptions = _.map(_.range(2, 45), function(page){
  var options = _.clone(masterOptions)
  options.body.page_num = page
  return options
})

Promise.map(allOptions, function(options){
  return Promise.resolve(options).delay(3000)
}).then(console.log)

or

Promise.map(_.range(2, 45), function(page){
  var options = _.clone(masterOptions)
  options.body.page_num = page
  return Promise.resolve(options).delay(3000)
}).then(console.log)

These do not seem to work, the options object seems to be iterating over the last produced object { body: { action: 'read', page_num: 44, page_size: 5 } } for each iteration.

How can I clone an object and iterate over one of it's properties?

Answer 1

Yes, you're right, Underscore 's clone function isn't deep .

This means that each property of the object you're cloning will be a new variable, but that variable will be populated simply by copying the content of the corresponding original one.

That is actually mentioned in the documentation for Underscore 's clone function (link) . Here's what is said:

Create a shallow-copied clone of the provided plain object . Any nested objects or arrays will be copied by reference, not duplicated.

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So, as you guessed, it seems that there's no out-of-the-box deep copy function in Underscore right now. Using cloneDeep as you mentioned in your comment will indeed resolve your issue :)