Code polishes

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For #165 code review, @jonathanolson and I discussed a couple of other potential polishes:

• More liberal use of type expressions for local vars (reduce code searches)
• Type expressions for this.fields defined at end of constructor (reduce code searches)
• Review calls to Property setDeferred
• Replace _.filter with built-in
• Replace _.map with built-in
• Replace for loops with map or forEach

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Done, closing.